IV. DlSCUSSlSONS

1. SIGNIFICANCE OF STOMATAL STUDIES

A deta i led study i n stomata has been done on Angiosperm

fami l i es such as Magnoliaceae (Pa l iwa l and Bhandari , 1962: A v i t a

and lnamdar, 1981b); Piperaceae (Pant and Baner j i , 196%);

Celastraceae (Pant and Kidwai , 1966); Ranunculaceae (Pant and

Mehra, 1963); Capparidaceae ( A l e y k u t t y and lnamdar, 1978);

Lauraceae and Paeoniaceae ( A v i ta and lnamdar, 1980, 1981 a, b ) . I n Compositae stomata1 studies have been c a r r i e d out b y Metcalfe

and Chalk (1950).

Stomata o f d i f f e r e n t types are not iced i n the leaves o f a

s ingle plant. Th is condi t ion i s repor ted i n many p lants (Metcalfe

and Chalk, 1950, 1979; Webster, 1956, 1958; Pant and Kidwai,

1964; Pal iwal, 1966; Pant and Baner j i , 1965~ ; Inamdar, 1969a.

, 1970; lnamdar and Patel, 1976; Raju and Rao, 1977, 1987;

Baas - - e t al., 1982; Baranova, 1986,1992). The predominant t y p e

anomocytic stomata are seen i n association w i t h a few stomata of

o the r types. E a r l i e r , t h i s condi t ion was repor ted i n Olacaceae

(Baas - e t - at., 1982); Buxaceae (Baranoa, 1980); Chloranthaceae

(Baranoa, 1986) and i n many o ther d ico ts b y d i f f e ren t authors.

According to Metcalfe and Cha lk (19501, stomata of

Compositae a re most ly anomocytic to anisocyt ic . The present

observat ion recorded f i v e types o f stomata. They a re anomocytic,

an isocy t ic , d iacy t i c , p o l o c y t i c and hemiparacyt ic . Anomocytic and

an isocy t ic t ypes o f stomata a r e most commonly observed i n

m a j o r i t y o f taxa studied. In a d d i t i o n to these. two d i a c y t i c

stomata a r e a lso no t iced i n a l l t h e f i v e Spi lanthes Jacq. s tudied.

The p o l o c y t i c stomatal t y p e o f f e r n s are r e p o r t e d i n some fam i l i es

o f f l ower ing p lan ts l i k e Onagraceae and Caryophy l laceae ( F r y n s - Classens and VanCotthom, 1973; Pant, 1965). Po locy t i c stomata

were r e p o r t e d i n - Tacca b y L i n g (1981). I n t he present

inves t iga t ion p o l o c y t i c stomata a r e no t iced i n the leaves of

Wedelia ch inensis (Osbeck) Merr..

The presence o r absence o f stomata on t h e ep ide rm is of

leaves i s ex t reme ly useful i n de l ineat ing tax3 b o t h a t t he species

and gener ic leve ls . Leaves o f a l l t h e taxa s tud ied a r e

amphistomat ic except i n Montanoa b i p i n n a t i f i d a C. Koch and

Wedel ia u r t i c i f o l i a DC., where the leaves a r e hypostomat ic .

The t y p e o f stomata i s a lso o f cons iderab le s igni f icance i n

d e l i m i t i n g t h e taxa, b o t h a t t he species and generic levels . F o r

example, t he dominant t y p e o f stomata i s anomocyt ic o r an i socy t i c

i n t h e leaves o f Wedelia u r t i c i f o l i a DC. and Wedelia t r i l o b a t a (L.)

AS. Hith.. In a d d i t i o n to these two types, p o l o c y t i c and

hem ipa racy t i c stomata are observed i n Wedel i a ch inensis (Osbeck)

Merr.. The d i f f e r e n t species o f Spi lanthes Jacq. possess d i a c y t i c

stomata as t h e most f requent type.

P r i m i t i v e t y p e o f stomatal complex i n angiosperm i s

p a r a c y t i c (Takhtajan, 1966). T h i s i s suppor ted b y Cronquist

( 1 988). Thomas and Bancrof t (1 91 3 ) d i scove red Rubiaceous stomata

i n Bennett i . tales. It i s s ign i f i can t to note tha t p a r a c y t i c stomata

a r e of r a r e occurence i n t h e t r i b e Hel iantheae and t rans i t i ona l

t y p e o f stoma (hemipa racy t i c ) was observed i n on l y one taxon

under s tudy - Wedelia ch inensis (Osbeck) Merr.. However, t h e

p r i m i t i v e stomatal complex i s a debatable question, since a l l t h e

stomatal t ypes occur i n t h e p r i m i t i v e as w e l l as h i g h l y advanced

fami l ies .

Some o f t h e unusual forms o f stomata r e p o r t e d i n t h e

present inves t iga t ion a r e (1 ) ' p e r s i s t e n t stomatal c e l l (2 )

s ing le guard c e l l w i t h o r w i thou t p o r e (3) abor ted guard c e l l s

( 4 ) contiquous stomata ( 5 ) cy top lasmic connection between

nearby stomata ( 6 ) guard c e l l s unusual ly nar row ( 7 ) guard

c e l l s o f unequal s i ze and ( 8 ) adjacent stomata w i t h common

s u b s i d i a r y c e l l s .

Stornatal i ndex

l'harmacognos~ists' have made successfuI e f f o r t s to use the

number o f stomata p e r u n i t area o f leaf sur face as a d iagnost ic

cha rac te r f o r f ragmentary mater ia l (Wilk insons, 1979). Sa l i sbu ry

(1927) in t roduced t h e te rm stomatal index t o express stomatal

f requency independent o f t h e s ize o f t h e ep idermal ce l l s . Though

many o f t h e contemporary bo tan is ts c r i t i c i s e d t h e r e l i a b i l i t y o f

stomatal f requency and stomata1 index (Stober, 1917; L o f t f i e l d ,

1921 and Timmerman, 1927). care fu l observat ions made b y Rowson

(1943a. 1943b. 1946). re-emphasised t h e use o f stomatal index i n

pharmacognocy .

Wilk inson (1979) po in t s out t h a t t h e stomatal i ndex i s a

usefu l taxonomic cha rac te r when comparable l ea f areas are used.

The taxa co l l ec ted f rom d i f f e r e n t l o c a l i t i e s showed more o r less

constant stomatal i ndex values and can be used i n d i s t i ngu i sh ing

d i f f e r e n t taxa. Compared to the adax ia l sur face o f t h e leaf,

stomatal index values are found to b e h i g h on the abax ia l sur face

o f a l l t h e inves t iga ted taxa. On t h e abax ia l sur face t h e h ighes t

and lowest stomatal i ndex values are no t iced i n T r i d a x procumbens

L. (30.64) and Xanthium indicum (13.57) respec t i ve l y . On t h e

adax ia l sur face t h e h i g h e s t and lowest values a r e 23.93

(He1 ianthus l a e t i f l o r u s Pers. and 3.96 (Sigesbeckia o r i en ta l i s L . )

respec t i ve l y . Eventhouqh t h e stomatal index values are constant fo r

taxa, due to ove r lapp ing and r e p e t i t i o n o f values, t h i s c r i t e r i o n

i s not a p p l i c a b l e f o r taxonomic purposes.

Stomata1 f requency

According .to Stace (1965a,b,1981) t h e d i s t r i b u t i o n and

f requency o f stomata are usefu l i n so l v ing prob lems o f

systemat ics. Sa l i sbu ry (1927) emphasized t h a t t h e f requency of

stomata i s h i g h when t h e s i ze o f t h e ep idermal c e l l s i s low and

t h a t t he frequency i s low when t h e ep ide rma l c e l l s a re large.

L o f t f i e l d (1921) l i k e w i s e found t h a t t h e stomata1 frequency i n

Malva r o t u n d i f o l i a L. i s u n r e l i a b l e f o r

p resent s tudy suggests t h a t , stomatal

taxonomic value, since t h e same taxon

shows v a r i a t i o n i n t h e stomatal f requency.

2. DIVERSITY I N LEAF ARCHITECTURE AND ITS SIGNIFICANCE

In Angiosperm f a m i l i e s lea f a r c h i t e c t u r a l s tud ies have

been done b y many researchers v iz . , Ke rne r and O l i v e r ( 1985 ) ;

Foster (1950, 1952, 1959, 1961, 1963, 1966 , 1968, 1970 ) ; Hickey

( 1 9 7 3 ) ; M e l v i l l e ( 1 9 7 6 ) ; Hickey and Wolfe ( 1 9 7 5 ) . Venation

s tud ies have been c a r r i e d out b y Banerjee and Deshpande ( 1 9 7 3 ) ;

Banerjee ( 1 9 7 8 ) i n c e r t a i n members o f Compositae.

SehgaI and Pa l iwa l ( 1974 ) c l a s s i f i e d leaves as uni -, b i - and tri - ve ined on t h e bas is o f t h e number o f s t rands enter ing

t h e base o f t h e pe t i o l e . In t he present s tudy , leaves a r e most ly

t r i - v e i n e d . But i n t he members o f t h e s u b t r i b e Coreopsideae

s ing le m i d r i b en te rs t he base o f t h e p e t i o l e and serves as the

o r i g i n f o r t h e h i g h e r o r d e r venation. I n a l l t h e cases t h e ve ins

a r e mu l t i se r i a te .

M a j o r venat ion p a t t e r n i s mos t l y o f Acrodromous t y p e in

t h i s t r i b e . But t h e taxa coming under t h e s u b t r i b e Coreopsideae

shows Semicraspedodromous t y p e o f venat ion.

Marg ina l u l t i m a t e venat ion i s o f f i m b r i a t e t y p e i n m a j o r i t y

o f t h e taxa. But t h e species o f t h e s u b t r i b e Coreopsideae shows

in t ramarg ina l ve ins. It may b e t h e f i m b r i a t e v e i n w h i c h i s

fo rmed due t o t h e fus ion o f h i g h e r o r d e r veins, w h i c h runs just

i n s i d e the marg in l i k e t h e in t ramarginal ve in . \

103

L e v i n ( 1 9 2 9 ) has emphasized t h e taxonomic va lue o f ve in -

i s l e t areas and op ined t h a t v e i n - i s l e t number i s nea r l y constant

f o r a species and can b e used as a va luab le spec i f i c charac ter .

H a l l and M e l v i l l e (1951, 1954) po in ted out t ha t t he number o f

v e i n l e t terminat ion e i t h e r alone o r along w i t h o the r h i s to log i ca l

c h a r a c t e r s can b e used as a too l f o r assessing the p u r i t y o f

f ragments o f a p a r t i c u l a r known lea f . Gupta ( 1 9 6 1 ) i s o f op in ion

t h a t ve in - i s l e t and v e i n l e t t e rm ina t i on numbers a re i n v e r s e l y

p r o p o r t i o n a l t o t he area o f t he lamina. Varghese ( 1969 ) on t h e

b a s i s o f t he s tudy on venat ion p a t t e r n o f some Scrophular iaceae

p o i n t e d out t ha t t he number o f ve ' in - is le ts and ve in le ts are more

o r less constant f o r a species.

N ice l y ( 1 9 6 5 ) has o b s e r v e d s ign i f i can t va r i a t i on i n size,

shape and number o f ve in endings i n each v e i n - i s l e t o f t he same

leaf. Sehgal and Pa l iwa l ( 1 9 7 4 ) ; Singh - e t - al., ( 1 9 7 6 ) ; Jain

( 1 9 7 8 ) ; lnamdar and Mur thy ( 1 9 7 8 ) and Rao and lnamdar ( 1 9 8 3 )

concluded . t h a t the;e i s no c o r r e l a t i o n between t h e s i ze of an

a reo le and the number of ve in endings i n d i f f e r e n t species as w e l l

as i n t h e same species and t h e r e f o r e t h e chances of using these

cha rac te rs as tools i n consider ing t h e taxonomy o r phylogeny of a

t a x a i s ins igni f icant .

The present i nves t i ga t i on revea ls tha t ve in - i s l e t

numberlmm2, ve in le t enter ing number/mm2, ve in ending terminat ion

numberlmm2 a re more o r less constant f o r a species. But c l o s e l y

s i m i l a r va lues a r e repeated i n co-generic species and also i n

spec ies belonging to d i f fe ren t t r i b e s and genera l l y the values d o

not show much dev ia t ion w i t h i n t h e t r i b e (Tab le 5). Thus due t o

t h e ove r lapp ing and r e p e t i t i o n of values, t h i s c r i t e r i o n i s not

a p p l i c a b l e f o r taxonomic purposes.

The number o f v e i n endings a r e i n no way connected t o

t h e s i z e o f t h e areole as t h e nea rby areo leseven though more o r

less equal i n size v a r y i n t h e i r number o f ve in endings. The

a reo les may o r may not have v e i n endings and i n such cases loop-

l i k e s t ruc tu res a r e formed e i t h e r b y t rache ids o r ve ins wh ich

reduce t h e d is tance between t w o v e i n s and thus he lps i n

t ranspor ta t ions . Loop format ion . i s a common feature i n t h e

a reo les where the re a r e a few v e i n endings o r none. In t h e

p resen t s tudy loops are found i n t a x a l i k e Xanthium indicum J.

Koenig., Zinnia l i nea r i s Benth., B l a i n v i l l e a acmella (L.) Ph i l i pson

and Montanoa b i p i n n a t i f i d a C. Koch..

P r i n c i p a l and secondary o r minor v e i n endings a r e

o b s e r v e d i n dicot\ l ledons b y F i s c h e r (1885). P r i n c i p a l ve in

endings a r e usua l ly branched s t r u c t u r e and secondary ones s h o r t

o f ten w i t h i n a s ing le t rache id . S t ra in (1933) made a s tudy o f

x y lem s t ruc tu re o f ve in endings i n d i co ty ledons and es tab l ished

ca tegor ies o f ve in endings based on t h e number o f terminal

t r ache ids . H ickey (1933) c l a s s i f i e d t h e v e i n endings in to s imp le

and branched. S t ra in (1933) r e p o r t e d t h a t v e i n ending types i n

angiosperms were h i g h l y v a r i a b l e and cou ld not be used t o

d i s t i n g u i s h major taxa such as fami l ies .

The present s t u d y revea ls t h e presence o f b o t h p r i n c i p a l

and secondary v e i n endings i n d i f f e r e n t taxa. Simple and

branched v e i n endings are also met w i th . P r i n c i p a l v e i n endings

are most commonly obse rved i n E c l i p t a p r o s t r a t a (L.) L. Mant.,

Sigesbeckia o r i e n t a l i s L. and Xanthium ind icum J. Koenig. In a l l

t he f i v e species o f Spi lanthes Jacq. s tudied, the v e i n endings a r e

long and mos t l y d e v o i d o f terminal t r a c h e i d s . Bo th uni- and bi-

se r ia te t r a c h e i d s a r e no t iced at t he v e i n t i p s o f E c l i p t a p ros t ra ta

(L . ) L. Mant.. Therefore, v e i n ending t y p e and nature,

c h a r a c t e r i s t i c o f c e r t a i n genera have some s ign i f i cance along w i t h

marginal features. T rache ids a t t h e v e i n endings increase c e l l

d iameter and are e x t r a o r d i n a r i l y v a r i a b l e i n size, shape and

nature.

I so la ted f r e e v e i n endings and t r a c b e i d s a r e q u i t e common

i n many species s tud ied . Kasap l i g i l (1951) f o r t h e f i r s t t ime

r e p o r t e d t h e . :presence o f i so la ted v e i n endings i n Lauraceae. . Later many resea rche rs (Fos ter and Arnot t , 1960; Herbst, 1972;

Sehgal and Pa l iwa l , 1974) have repo r ted t h i s unique feature i n

many angiosperm leaves. lnamdar and M u r t h y (1981) c l e a r l y

exp la ined t h e " i s o l a t e d t rache ids " as tracheids, l y i n g f r e e i n t h e

areole; " i so la ted v e i n endings", a r e w i t h t rache ids . w h i c h a r e

l y i n g f ree i n t h e areole. Iso lated t r a c h e i d s a r e observed i n

E c l i p t a p r o s t r a t a (L . ) L. Mant., Wedelia ch inens is (Osbeck l Mer r .

and Synedrel l a n o d i f l o r a (L. ) Gaertner.

Hara (1962) r e p o r t e d some elongated c e l l s termed as

"extension c e l l s " between one vein and v e i n ending o f another

vein. S im i l a r ex tens ion c e l l s are found i n Lagascea m o l l i s Cav.,

Melampodium paludosum B.H. K., and i n a l l t h e Spi lanthes Jacq.

s tudied. A l l t h e ma jo r ve ins a r e jacketed by parenchymatous

bund le sheath i n most of t h e cases.

Hydathodes

Hydathodes have been repor ted as r a r e f o r t h e Asteraceae

(Solereder, 1908; Metcal fe and Chalk, 19501, e x c e p t a few repo r t s

i n taxa such as Senecio s a x i - f ragoides Hook. F. and S. laqopus -

Raoul (Wall, 1918).

C a r l q u i s t (1957, 1958) repor ted t h a t "mass ive hydathodes"

occur along lea f margins o f A r g y r o x i ~ h i u m c a l i g i n i i . In Launaea

asp len i fo l ia , Banerjee and Deshpande (1973) mere l y dep ic ted th ree

converging ve ins p e r leaf tooth. Hydathodes i n lea f tee th o f th ree

arborescent Scenecio soecies was r e p o r t e d by Hare (1941).

Fentzke (1920) has r e p o r t e d about the n a t u r a l l y gu t ta t ing p lan t bu t

did not desc r ibe hydathddes. A poss ib le hyda thode va r ian t was

h i n t e d a t by Henr ickson (1976). who not iced that, i n t h e monotypic

dese r t s h r u b Marsha l l johns ton ia (Lactuaceae), l ea f teeth are

"achIorophyI Ious, s t rong ly vasculated, and deve lop a d i s t i n c t i v e

w h i t e encrustat ion o f an undetermined noncrysta l l i n e mater ia l ove r

t h e i r surfaces". Recent ly hydathodes a r e r e p o r t e d i n cer ta in

members o f Asteraceae by Lersten and John C u r t i s (19851.

I n t h e o resen t s tudy hydathodes a r e no t i ced i n a l l the 38

taxa studied. T h e y a r e ma in l y located a t t h e marg ins and t i o of

t h e leaves exceot i n Coreopsis g rand i f l o ra Hogg. where i t i s found

o n l y a t t h e tip.

3. VARIATIONS I N PALISADE RATIO AND TAXONOMY

The use o f pa l i sade r a t i o i n d iagnost ic purposes i s w e l l

e s t a b l i s h e d by Zorning and Weiss (1925). Wal l i s and Dewar (1933).

W a l l i s and F o r s d i k e (1938); Metcal fe a n d Cha lk (1979). According

t o Dewar (1933, 1934a. 1934b) and W a l l i s and Fo rsd i ke (1938) t h e

number o f pa l i sade c e l l s i s constant i n d i f f e r e n t par ts o f a l ea f

c o l l e c t e d f rom extreme ecological cond i t ions .

A separate s u b t r i b a l status i s g i ven t o Lagascea m o l l i s

Cav. by Bentham and Hooker (1876) and Hoffmann (1890). Stuessy

(1973) reduced t h i s s u b t r i b e and i nc luded t h i s taxa i n

Verbesininae. Robinson (1981) p l a c e d i t a longwi th h i s o t h e r

He l ian th inae members. The pa l i sade r a t i o va lue indicates t h a t i t

i s more o r less s i m i l a r to Robinson's ( I .c.) Hel ianthinae members. - -

I n t h e rev i sed c lass i f i ca t i ons Stuessy ( I .c.l and Robinson -- c . - - h a v e e f fec ted some in t ra . and i n t e r - t r i b a l t rans fer o f

genera. The genus Parthenium L. i s removed f rom t h e s u b t r i b e

Melarnpodieae and added t o Ambrosi inae i n t h i e r c lass i f icat ions.

It i s i n te res t i ng to note t h a t t h e p a l i s a d e r a t i o values o f b o t h

Par thenium L. and Xanthium L. a r e v e r y s i m i l a r and so present

f i ndg ins a r e i n con f i rm i t y t o t h e l a t e s t c lass i f i ca t ions .

4. SIGNIFICANCE OF HISTOCHEMISTRY

L i te ra tu re revea ls t h a t v e r y l i t t l e attent ion i s g iven t o

h is tochemical s tud ies o f stomata and epidermis. Meidner and

Mansf ie ld (1968). Rajagopal and Ramayya (1970). and Bhat t and

lnamdar (1975) s tated t h a t t h e h i s t o c h e m i s t r y o f t h e stomatal

complex i s incomplete ly known. The present work on 26 genera

and 40 species descr ibes t h e contents o f t h e stomatal apparatus

along w i t h t h e ep idermal c e l l s b y local izat ion o f var ious

substrates.

D i f fe ren t t ypes o f p l a s t i d s a r e present i n the l i v i n g c e l l s

o f h i g h e r p lants. A l l these p l a s t i d s a r e ab le to produce s t a r c h

[W ink le r , 1898). In t h e present study, s ta rch g ra ins a r e

obse rved .in gua rd ' c e l l s o f a l l t h e taxa. The range i s f rom a

minimum o f one i n Cuizot ia abyss in i ca (L.f.1 Cass. to a maximum

o f twenty i n Dah l ia p innata Cav.. Sav i t zky (1966) po in ted out

t h a t t h e large number o f c h l o r o p l a s t i n the guard ce l l s i n a sugar

cane va r ie t y , can be a t t r i b u t e d to te t rap lo idy . M u r t h y and

lnamdar (1980) r e p o r t t h a t i n Solanaceae the number o f s t r a c h

g ra ins in t h e guard c e l l s v a r i e s w i t h i n the fami ly , but i s

constant f o r a species. The present s tudy shows tha t t h e number

o f s t a r c h gra ins are more o r less constant f o r a saecies, bu t t h e

same taxon growing under d i f f e r e n t ecological s i tuat ions shows

s l i g h t d i f ference i n t h e number o f s t a r c h g r a i n s Re icha r t (1973)

has po in ted out t h e need o f a d e t a i l e d ana lys i s o f s t a r c h grains,

w h i c h can g i v e diagnost ic charac ters lead ing t o a s t r i c t l y

s c i e n t i f i c b a s i s f o r t he c lass i f i ca t i on o f p lan ts . The present

s t u d y shows t h a t mere l i g h t m i c r o s c o p i c s tud ies w i l l not p r o v i d e

s u f f i c i e n t ev idence i n t h i s respect .

T i k k u ( 19751 , T i k k u e t al., ( 1 9 7 8 ) a r e o f t h e opinion - - t h a t d i s t i n c t i o n o f subs id ia ry c e l l s f rom o t h e r ep idermal c e l l s

w i t h 12Kl - H SO tes t i s p o s s i b l e i n monocots. M u r t h y and 2 4

lnamdar ( 1 9 8 0 ) . lnamdar and Rao ( 1 9 8 2 ) p r o v e d t h a t t h i s test i s

u s e f u l i n i d e n t i f y i n g the s u b s i d i a r y c e l l s i n dicotyledonous

f a m i l i e s too. The present s tudy i s no t i n accordance w i t h these

f i n d i n g s as t h e epidermal c e l l s and s u b s i d i a r y c e l l s reac t

i d e n t i c a l l y .

W i t h PAS, guard cel ls , s u b s i d i a r y c e l l s and epidermal

c e l l s reac t p o s i t i v e l y g i v ing un i fo rm resu l t s . T h i s t e s t i s not

use fu l f o r i d e n t i f y i n g t h e s u b s i d i a r y c e l l s . Insoluble

po l ysacchar ides o c c u r . i n d i f f e r e n t fo rms viz., granular and

amorphous i n t h e d i f f e r e n t taxa s tud ied . Hinchman ( 1 9 7 3 ) i s of

t h e op in ion t h a t t h e r a t i o o f po l ysacchar ides v a r i e s cons iderab ly

depending on t h e species o r c u l t i v a r , t h e locat ion and m a t u r i t y o f

t i ssues and o t h e r factors. Since t h e resu l t s o f t h e staining

reac t ions a r e dependent on var ious in te rna l as w e l l as external

fac tors , no general isat ion can b e made w i t h rega rd to t h e

constancy o f t h e reac t ion w i t h i n a species.

Tolu id ine b l u e ' 0 ' (TBO) g i v e s d i f f e r e n t i a l s ta in ing

react ions f o r su lpha ted and ca rboxy l a t e d po lysacchar ides and

polyphenols. Perigenous subs id ia ry c e l l s react p o s i t i v e l y w i t h

su lphated and c a r b o x y l a t e d po l ysacchar ides and mesogenous

s u b s i d i a r y c e l l s r e a c t p o s i t i v e l y f o r oo l ypheno ls w i t h TBO.

Esau (1977) comments tha t w i t h rega rd to p lan t par ts ,

w h i c h no rma l l y b e a r c e l l s have pheno l ic depos i ts bu t no t issue

lacks po lypheno ls e n t i r e l y . In t h e present s tudy phenol ics are

obse rved i n t h e ep ide rma l t issues o f a l l t h e taxa studied. Being

a q u a l i t a t i v e test, no c la im i s being made on t h e complete absence

o f pheno l i c compounds i n t h e ce l l s o t h e r than those spo t ted i n the

s tudy , bu t emphasis i s g iven t o t h e r e l a t i v e d i s t r i b u t i o n and

concentrat ion o f these compounds i n t h e ep idermal pa r t s .

The d i s t r i b u t i o n of phenol ic compounds i s un i fo rm w i t h i n

a genus. But an increase i n the pheno l ic content i s noted dur ing

t h e d r y season. T h i s i s i n accordance w i t h t h e r e p o r t s o f Gr ieve

(1953). t ha t p lan ts growing i n d r y cond i t ions have h i g h phenol ic

content. Theunissen (1990) has a lso suppor ted t h i s v iew.

Present s tudy con f i rms t h a t environmental f ac to rs have great

inf luence on t h e d i s t r i b u t i o n and concentrat ion o f pheno l ic

compounds.

Phenol ics a r e present main ly i n ep idermal t issues. But

not Ioca l ised i n t h e s u b s i d i a r y c e l l s o f c e r t a i n taxa. Theunissen

(1990) has emphasised t h a t presence o f pheno l i cs i n the

s u b s i d i a r y c e l l s i s con t ro l l ed b y ce r ta in genes. T h e absence of

p h e n o l i c s i n cer ta in taxa may be due t o the genetic influence.

F u r t h e r w o r k i s y e t t o be done r e g a r d i n g t h i s point .

Pate l (1978) descr ibes t h e s ign i f i cance of h i s tochemis t r y

as an a i d t o the ident i f i ca t ion o f s u b s i d i a r y cel ls. TBO tes t

h e l p s t o d i f f e r e n t i a t e the s u b s i d i a r y c e l l s due t o i t s se lec t i ve

s t a i n i n g react ions f o r the l oca l i sa t i on o f pheno l ics and sulphated

and c a r b o x y l a ted p o l ysaccharides. Thus h i s tochemis t r y h e l p s t o

s t u d y t h e ontogeny r a t h e r than morpho logy .

The c e l l w a l l s and nucleus o f c e l l s and tr ichomes o f a l l

t h e i nves t i ga ted taxa react pos i t i ve1 y w i t h mercur ic bromophenol

b l u e i nd i ca t i ng the presence o f p ro te ins . Tha le r (1955) desc r ibed

g i a n t p ro te ino p l a s t i d s in t he e p i d e r m a l c e l l s o f Hel leborus

c ras i cus WiIId.. I n taxa l i k e . Lagascea m o l l i s Cav. nucle i a r e

sur rounded b y 5-7 p ro te in bod ies (P1.16 : 0 ) . According to

Swain (1963). some o f t he p l a s t i d s a r e a b l e t o produce o i l s o r

p r o t e i n s as t h e i r f i n a l p roduct . A l l t h e p l a s t i d s i n the gua rd

c e l l s o f t h e inves t iga ted taxa showed t h e presence o f prote ins.

Ce r ta in minute sudan dyes p o s i t i v e l ip id granules a r e

o b s e r v e d i n t h e cytoplasm o f s u b s i d i a r y c e l l s and epidermal c e l l s

o f t h e taxa studied. Ce l l wa l l s a l s o showed p o s i t i v e react ion

i n d i c a t i n g t h e presence o f l i p i d s . Pate l - et - al., (19751

d i s t i n g u i s h e d the s u b s i d i a r y c e l l s f rom o t h e r epidermal c e l l s b y

t h e absence of l ip id bodies i n A r t h r o m e r i s wal l ich iana. The

r e v e r s e cond i t ion i s observed i n some members of Zingi beraceae

(Ra ju and Shah, 1975). In t h e p resen t s tudy subs id ia ry c e l l s

cannot be d i s t i ngu i shed f rom e p i d e r m a l ce l I s because o f t h e

u n i f o r m a c t i v i t y of t h e s ta in on bo th .

5. STRUCTURAL VARIATION I N VESSEL ELEMENTS AN0

ITS SIGNIFICANCE

The xy lem occupies a unique pos i t i on among t h e p l a n t

t issues because i t s anatomy i s ex t reme ly useful i n assessing

taxonomic re la t i onsh ips and e l u c i d a t i n g p h y Iogeny (Metcal fe and

Chalk, 1950; Swamy e t al., 1960; Car lqu i s t , 1961). W i th in t h e - - x y l e m tissue, the vessel element h'as been considered as k e y u n i t

o f t h e xy lem f rom the evo lu t i ona ry po in t o f v i e w (Car lqu i s t ,

19621. Although a general account on t h e anatomy o f Compositae

has been p u b l i s h e d b y M e t c a l f e and Cha lk (1950) and C a r l q u i s t

(1966). no d e t a i l e d inves t iga t ions on d i f f e r e n t facets o f vessel

elements i n t he f a m i l y h a v e been c a r r i e d out. A s tudy on

morphology o f noQI, i n te rnoda l and root vessels, na ture and

arrangement o f p i t s and p e r f o r a t i o n p la tes in d i f f e r e n t organs o f

39 taxa has the re fo re been c a r r i e d out, and t h e resu l t s a r e

d iscussed as under i n t h e l i g h t o f re levan t pub l i shed l i t e ra tu re .

Radford e t al., (19711) c l a s s i f i e d the vessel elements i n t o - - 7 classes based on t h e i r length. Vessel elements o f t h e d i f f e r e n t

taxa studied f a l l under s i x classes, v iz . , ex t remely s h o r t

(. <175 p m ) , v e r y s h o r t (1 75 - 250 pm) , moderate ly s h o r t (250 -

350 pm) , medium s i zed (350 - 800 p m ) , moderate ly long (800 - 1100 pm) and v e r y long (1100 - 1900 p m ) .

Accord ing to Metcalfe and Cha lk (1950) vessel elements o f

Compositae a r e t y p i c a l l y smal l (( 100 p m l . The present s tudy

r e v e a l s t h a t o f t h e 6 d i f f e ren t classes, v e r y sho r t , moderate ly

s h o r t and medium s ized vessels a re commonly observed i n t he

in te rnode and roo t o f most o f t he taxa. I n node, ex t reme ly sho r t

and v e r y s h o r t t y p e o f vessels a r e most commonly observed.

Modera te l y long, and v e r y long vessel 'e lements , however, are

present in low f requency i n d i f f e r e n t organs o f a few taxa and

hence t h i s t y p e i s o f l i t t l e signif icance.

Based on diameter, t h e vesse l elements a r e grouped into 7

c lasses (Rad fo rd - e t - al., 1974). T h e y a r e ex t reme ly small

((25 p m ) , v e r y s m a l l (25- 50 pm) , modera te l y smal l (50-100 p m ) ,

med ium-s ized (100-200 p), modera te ly la rge (200-300 p ) , v e r y

la rge (300-400 p ) and ex t remely l a r g e ( 7 4 0 0 )rm). According t o

t h i s c lass i f i ca t i on , t h e d iameters o f vesse l elements s tudied

belong to . t h e f i r s ? 3 classes. Very smal I, modera te ly smal l and

medium - s i z e d vessel diameters a r e f requent1 y observed in t h e

internode, node and r o o t o f most o f t h e taxa invest igated.

The vesse l length i s c o r r e l a t e d w i t h t h e h a b i t and has no

apparent r e l a t i o n s h i p w i t h e i t h e r taxonomy o r phy logeny o f taxa.

The woody p l a n t s have comparat ive1 y s h o r t e r and w i d e r vessels,

whereas herbaceous taxa have longer and nar rower ones.

According t o C a r l q u i s t (1966) t rees have l a r g e r vessel elements

than shurbs, and t h e shrubs have l a r g e r vesse ls than herbs i n

Compositae. The present s tudy conf i rms t h e f i n d i n g s o f Car lqu is t

(1.c.). -- Compara t i ve l y long and na r row vesse l elements are

obse rved i n T r i d a x procumbens L..

Regarding the shape, c y l i n d r i c a l f o rm i s observed in

m a j o r i t y o f t h e species. Var iat ions a re more i n nodal region than

i n o t h e r regions. T h i s may be due to the branch ing and fusion

o f t h e vascu la r bundles a t the nades. I n node ex t remely shor t

and v e r y s h o r t t y p e o f vessel elements a r e commonly observed.

T h i s can b e exp la ined b y the s h o r t length and congestion a t the

node as has been po in ted out b y Cheadle (1943a. 1943b).

I n Compositae per forat ion p la tes a r e t y p i c a l l y simple

(Metcal fe and Chalk, 1950). Sca lar i fo rm and re t i cu la te types o f

pe r fo ra t i on p l a t e s a r e repor ted b y Solereder (1908) and Smith

(1935). Ret icu la te per fora t ion p l a t e i s obse rved in some taxa,

b u t sca la r i f o rm t y p e i s v e r y r a r e l y observed d u r i n g the course of

invest igat ion. Smith (1935) has po in ted out the mul t iper forated

t y p e o f the p l a t e s i n the xy lem vessels o f Hel ianthus annuus L..

But i n t h i s taxa, on l y s imple t y p e o f pe r fo ra t i on p lates are

observed d u r i n g the study. Foraminated and sca la r i f o rm types o f . per fo ra t i on p l a t e s a re r a r e l y observed i n Xanthium indicum J.

Koenig. I t appears that the s imple pe r fo ra t i on p l a t e might have

e v o l v e d f rom sca la r i f o rm o r re t i cu la te t y p e by reduct ion in the

number o f ba rs . Such an evolut ionary t rend has been observed i n

Xanthium ind icum J. Koenig (P1.19 : K). Per fora t ion p lates

w i t h p a r t i a l l y b roken ret iculum i s noted i n Spi lanthes c i l i a t a H.B.

K. and - S. rad icans Jacq. (Fig.13 : 29.34.36). Reticulate and

s imp le p e r f o r a t i o n p la tes a t two ends o f t he same vessel element

a re observed i n Spi lanthes oleracea L., Bidens h u m i l i s H.B. K.

and - B. p i l o s a L. (Fig.13 : 30; Fig.14 : 1,11,131.

The number o f p e r f o r a t i o n p la tes p e r vessel var ieSf rom

one t o t h r e e w i t h two as t h e commonest number [Tab le 14.15 and

16 ) . The or ien ta t ion o f t h e p e r f o r a t i o n p l a t e may range f rom

o b l i q u e t o transverse.

In te rvascu lar p i t t i n g i s m o s t l y simple. However, vessel

elements w i t h bo rde red p i t s a r e obse rved i n a few taxa (Tab le

14.15 and 16 ) . The arrangement o f p i t s a re most ly a l ternate.

H o r i z o n t a l l y elongated p i t s a r e no t i ced as in Wedelia ch inensis

(Osbeck) Merr. and E c l i p t a p r o s t r a t a (L.) L. Mant.. Rare ly

o p p o s i t e and sca la r i f o rm p i t t i n g s a r e not iced. T h i s feature i s o f

evo lu t i ona ry signif icance, s ince sca la r i f o rm arrangement i s

p r i m i t i v e leading t o t h e s p e c i a l i z e d a l t e rna te arrangement th rough

oppos i te pat tern. Hel ica l p i t t i n g i s a lso not iced as i n Cuizot ia

abyss in i ca (L.f.) Cass.. In t h e p r e s e n t s tudy p i t s show v a r i a t i o n

i n size, shape and d i s t r i b u t i o n .

The s igni f icance o f t a i l i n vesse ls i s d i f f i c u l t t o def ine. . They may ' be seen a t one o r b o t h t h e ends o f t h e vessel elements.

T a i l s a r e seldom observed i n t h e c u l t i v a t e d p lants.

Vessels f rom d i f f e r e n t p a r t s viz. , node, in ternode and

r o o t s show d i f fe rences and s i m i l a r i t i e s i n t h e i r size, shape,

na ture and pos i t i on o f p e r f o r a t i o n p l a t e s and p i t s . Such

v a r i a t i o n s are noted even w i t h i n t h e l i m i t s o f a single species.

T h i s suppor ts t h e v i e w o f B a i l e y and Tupper (1918). who h a v e

stated . t ha t the vessel members f luc tua te w i t h i n the l i m i t s o f a

s i n g l e p lant . These ove r lapp ing nature o f var ia t ions encountered,

makes t h e observed v a r i a b i l i t y o f l i t t l e taxonomic signif icance.

Scanning electron micrograph o f t h e pol len grain o f Melampodium

paludosum B.H.K. (X55 .000 ) .

6. PALYNOLOGY AND ITS TAXONOMIC SIGNIFICANCE

T h e s t u d y o f p o l l e n m o r p h o l o g y h a s assumed g r e a t

s i g n i f i c a n c e i n t h e r e a l m o f m o r p h o l o g i c a l and c o m p a r a t i v e botany,

d u r i n g t h e l a s t t h r e e decades due t o t h e r e a l i s a t i o n t h a t t h e p o l l e n

g r a i n s r e f l e c t i n t h e m t o a f a i r d e g r e e t h e f a c t s and face ts o f t h e

b i o l o g y o f t h e m o t h e r p l a n t t h e y b e l o n g to . P o l l e n g ra in , one o f

t h e r e p r o d u c t i v e p a r t n e r s , i s more c o n s e r v a t i v e a n d r e g a r d e d as a

d e p e n d a b l e t o o l t o p l a n t taxonomy, phy Iogeny and e v o l u t i o n

( E r d t m a n , 1952; Saad, 1972; N a i r , 19711; W a l k e r and Doyle, 1975).

A c l e a r p i c t u r e o f t h e m o r p h o l o g i c a l c o n f i g u r a t i o n o f t h e e x i n e i n

t h e C o m p o s i t a e has been p r o v i d e d by Wodehouse (19351, w h i c h

h a s s e r v e d as an i n d e x f o r r e s e a r c h e r s s i n c e then. A p a r t f r o m

t h i s , a t t e n t i o n h a s a l s o been p a i d t o t h e p o l l e n m o r p h o l o g y i n

r e l a t i o n t o t h e taxonomy o f t h e f a m i l y by E r d t m a n (1952) and S t i x

(1960) . V a r i o u s o t h e r aspec ts o f p o l l e n b i o l o g y w h i c h h a v e

r e l e v a n c e t o t h e p o l l e n m o r p h o l o g y such as harmomegathy (Payne,

1972). s t r a t i f i c a t i o n o f p o l l e n w a l l ( S t i x , 1960). h i s t o c h e m i s t r y o f

e x i n e (Hes lop -Har r i son , 1971) and d e v e l o p m e n t o f e x i n e w a l l

( S k v a r l a a n d Larson, 1965a.b; R o w l e y and D a h l , 1977) h a v e a lso

been i n v e s t i g a t e d . A c r i t i c a l r e v i e w o f t h e p o l l e n m o r o h o l o g y i n

r e l a t i o n t o taxonomy and e v o l u t i o n o f t h e f a m i l y h a s been

p r o v i d e d by S k v a r l a - e t - al., (1977). A n a l y t i c a l s t u d i e s o f p o l l e n

m o r p h o l o g y i n r e l a t i o n t o taxonomy and p h y l o g e n y o f a n g i o s ~ e r m s

h a v e been made b y Na i r (1969, 1970, 1972a,b, 1979).

In Heliantheae, St ix (1960) examined s i x genera and

r e f e r r e d them to t h e Hel ianthus po l l en type. F e l i p p e and

L a b o u r i w (1964) extended t h i s w o r k to inc lude nine genera and 18

species. The present s tudy inc ludes t h e po l len morphology o f 38

t a x a belonging to 26 genera us ing b o t h l i g h t and scanning e lect ron

microscopy.

I n making morpho log ica l ana lys i s o f ex ine characters, and

a q p l y i n g them to taxonomy and evolut ion, i t i s now considered

t h a t characters re la t i ng to t h e ape r tu re are p r imary , o f ex ine

ornamentat ion. secondary, and o t h e r characters t e r t i a r y i n t h e i r

degree o f importance (Nair , 1965). The form, number and

d i s t r i b u t i o n o f t h e po l len g r a i n ape r tu re are t h e least changing

cha rac te rs [Na i r , 1965). They e x h i b i t va r i a t i on a t d i f f e r e n t

l e v e l s o f taxonomic h i e r a r c h y and hence are useful in t h e . identification of d i f f e r e n t taxa a t var ious taxonomic l eve l s

(Erdtman, 1952). In the present inves t iga t ion most o f t h e g ra ins

a r e 3-zonocolporate, in a d d i t i o n t o w h i c h (2)zonocolporate g ra ins

a r e r a r e l y observed in taxa such as Zinnia l i nea r i s Benth. and

Cosmos b ip innatus Cav. (PI.20 : P) . 4-zonocolporate gra ins a r e

no t i ced in T r i d a x procumbens L. and Spi lanthes oleracea L. (PI.20

: M, J l . Grains are 3,4-zonocolporate as in Spi lanthes Jacq.,

B idens h u m l l i s H.B. K . and B l a i n v i l l e a acmella L. Ph i l ipson.

In t h e colporate g r a i n s t h e endocolpium versus t h e

ectocolp ium i s often an i l l p o r t a n t cha rac te r i s t i c , t h e l a t t e r being

no t so impor tan t as t h e former. I n t h e o r d e r o f phy logenet ic

importance, t h e gra ins w i t h la-longate endocolpium i s advanced o v e r

c i r c u l a r . I n the present study, m a j o r i t y o f t h e gra ins are w i t h

la-Iongate endocolpium except i n Par then ium hys terophorus L.,

w h e r e it i s c i r c u l a r (PI . 20 : D l . La-longate endocolpium i s

e i t h e r b r o a d l y lent icu late t o apiculate, n a r r o w l y Ienticulate. sub-

l en t i cu la te o r dumb-bel l shaped w i t h rounded o r acute la te ra l ends

i n va r i ous taxa s tud ied (See Tab le 17) .

According to N a i r and Sharma (19651 t h e ex ine

ornamentat ion pa t te rn may b e cons idered t o b e a useful charac ter i n

t h e d e l i m i t a t i o n o f genera and species. Granulate pa t te rn o f

i n t e r s p i n a l ex ine scu lp tur ing i s t h e mos t common t ype encountered

d u r i n g t h e present invest igat ion. It i s observed i n 18 species.

E x i n e i s punctate i n Melampodium paludosum B.H.K., SynedreIIa

n o d i f l o r a - ( L . ) Caertner, Calinsoga p a r v i f l o r a Cav. and T r i d a x

procumbens L., Cranulose i n Par then ium hysterophorus L.,

Sp i lan thes c a l v a DC. and Cosmos b ip inna tus Cav.. Smooth i n Zinnia - elegans Jacq., rugulate i n E leu theranthera r u d e r a l i s (Swartz) Sch.

and foveo la te i n Spi lanthes u l i g inosa Sw.. The i n te rsp ina l

s c u l p t u r i n g o f ex ine p r o v i d e s impor tan t information f o r t h e

taxonomic separat ion o f c lose l y r e l a t e d species o f t he same genera.

Among t h e four Spi lanthes Jacq. s tud ied , t h e sculptur ing i s

granulose i n S. ca l va DC., granulate i n S. c i l i a t a -- - H.B.K.,

r e t i c u l a t e i n S. oleracea L., m i l d l y g ranu la te i n S. radicans Jacq. - and foveo la te i n - S. u l ig inosa Sw.. Heslop-Harr ison (1969) has

r e p o r t e d rugose surface pa t te rn f o r Cosmos b ip innatus Cav.. But

t h e present obse rva t i on based on SEM s tud ies r e v e a l e d t h a t the

ex ine sur face i s granulose.

The s i l h o u e t t e o f t h e exine sur face as e x e m p l i f i e d between

adjacent excrescences i s a lso o f some s igni f icance. The space

between two spines ( In te rsp ina l cu rve ) i s U, V o r trough-shaped

i n var ious taxa examined. The d e p t h o f t h e curves may be

sha l low o r deep.

In a d d i t i o n t o t h e germinal aper tu re , t h e r e a r e also o ther

morpho log ica l cha rac te rs such as , ex ine ornamentat ion i n wh ich

evo lu t i ona ry phenomena a r e expressed. Accord ing t o Wodehouse

(19351 po l l en g ra ins w i t h t h i c k and h e a v i l y ornamented ex ine have

been cons idered to be p r i m i t i v e , w h i l e those w i t h t h i n un-

ornamented ( P s i l a t e ) o r l i g h t l y ornamented ex ine a r e considered to

be advanced. I n Heliantheae, ex ine i s g e n e r a l l y spinate.

Regarding t h i s aspect Heliantheae p o l l e n i s p r i m i t i v e .

Among t h e taxa o f Heliantheae, p o l l e n w i t h long elongate

sp ines w i t h exposed sp ine column base may b e cons idered to

p recede those w i t h concealed spine column base and w i t h p a r t i a l l y

and f u l l y deve loped basal cushion ( N a i r and Lawrence, 1985). In

t h i s regard advanced ex ine excrescences a r e obse rved i n Xanthiurn

ind icum J. Koenig,Parthenium hys te rophorus L., Gal insoga

p a r v i f l o r a Cav. and Dah l ia pinnata Cav. . O f these. Xanthiurn L.

shows the most advanced cond i t ion r e g a r d i n g t h e ex ine

ornamentation, where spines are reduced and sur face i s s c a b r a t e

i n appearance. Tuberulate ex ine sur face i s no t i ced i n Dahl ia -

pinnata Cav.. I n t h i s t axa seed se t t ing i s r a r e and t h i s may be -

due t o s t e r i l e po l l en . S t e r i l i t y may be because o f some

chromosomal abe r ra t i ons . Most of t h e taxa coming under sub t r i bes

Verbesineae and Coreopsideae have po l l en w i t h conspicuous basal

cushions b u t t h e i r columns a r e longer.

The t h i c k n e s s o f t h e ex ine v a r i e s i n d i f f e r e n t taxa under

s tudy. It v a r i e s f rom 15.86 pm (Dah l ia i m p e r i a l i s Roezl.) to

5 .85 pm i n Synedre l l a n o d i f l o r a (L.) Caertner .

The s i ze and shape of . po l l en gra ins a r e o f l i t t l e

s igni f icance i n taxonomy. However, t h e s i ze and shape o f po l l en

gra ins are useful i n c e r t a i n instances, e s p e c i a l l y as an index o f

aneuplo idy o r when c o r r e l a t i n g w i t h chromosome number (Could,

1957). Sun (1946), c l a s s i f i e d the taxa Brass ica ,based on the s ize

o f t he p o l l e n gra in . Erdtman (1952) s ta ted t h a t t he v a r i e t a l

d i f f e rence i n p l a n t s can sometimes be r e f l e c t e d i n t h e i r oile en

gra in . ~e c l a s s i f i e d t h e po l l en gra ins i n t o s i x s i z e classes. In

t h e present i nves t i ga t i on the ma jo r i t y o f t h e taxa come under t h e

category medium s i z e c lass (25-50 pm] . Small (10-25 )lm) gra ins

a lso no t iced as i n Par thenium hys terophorus L. (21 pm).

The shape o f t he po l l en gra ins i s u n f i x e d and hence it i s

no t r e l i a b l e in t h e morphological ana lys is . A l though t h e pol len

gra ins are most conse rva t i ve against t h e f l uc tua t i ng environmental

condit ions, p o l y m o r p h i s m w i t h respect to d i f f e r e n t morphological

cha rac te rs o f p o l l e n g r a i n s has been known t o occur in many

p lan ts ( N a i r and Sharma , 1966-67). D imorph ism o r po lymorph ism

of p o l l e n gra ins e i t h e r occurs n a t u r a l l y o r due to var ious

envi ronmental o r nu t r i t i ona l s t ress.

Dimorphism w i t h respect t o t h e number o f aper tu re o f the

po l l eng ra ins was observed i n some o f t h e taxa s tud ied as

d i scussed e a r l i e r . Morpho log ica l l y two d i f f e r e n t types o f po l l en

g r a i n s are met w i t h i n Zinnia l i n e a r i s Benth. and Calinsoga

p a r v i f l o r a Cav.. Po l len w i t h sp inu la te o r tubercu la te ex ine surface

i s no t i ced i n - 2. l i nea r i s Benth.. Whereas i n - C. p a r v i f l o r a Cav.

sp ina te and spinulate types o f g ra ins a r e observed.

Koul (1969) has suggested t h a t d i m o r p h i s m f o r the number

o f a p e r t u r e may be genetical. N a i r and Sharma (1962) have made

an ex tens i ve s tudy on the po l l en morpho logy o f Argemon mexicana

and reached t h e conclusion tha t d i f f e r e n t g e o g r a ~ h i c a l d i s t r i b u t i o n

causes po l ymorph ism o f po l l en g ra ins . ~ n v i r o n m e n t a l o r

n u t r i t i o n a l f luctuat ions (Bel l , 1959) developmental factors (Clausen, 7

1962) and' genet ical d i f fe rence between popu la t ion (Could, 1957)

a r e some o f t h e factors .for t h e d i m o r p h i s m o f po l l en grains.

From t h e foregoing account i t may b e noted t h a t the

sys temat i c s tatus of var ious sub t r i bes and genera according to t h e

p o l l e n morphology w h i c h t h e y represent does not seem to f i t w i t h

t h e phy logene t i c and systematic s ta tus assigned to them b y

Bentham and Hooker, (1876). T h i s aspect i s discussed i n t h e sub

sec t ion sys temat ic considerat ion o f t h e t r i b e .

T h e form, number and d i s t r i b u t i o n o f t h e pol len g r a i n

a p e r t u r e a r e t h e leas t changing c h a r a c t e r s ( N a i r , 1 9 6 5 ) . So

u t i l i s i n g t h e palynological evidences f rom the present work , a

k e y i s p r o v i d e d f o r the t a x a under s t u d y .

KEY TO THE SPECIES

Cralns 3-ronocolporsle

Endocolplum l a l ~ n g a t e

C l rcu la r

Narrswly lenl lculete

Basal cushlon oramlnent

Intar-solnal area favaolala

In ler -sp lna l area granulate

Splne he lgh l ! 3.53 pm

Splne helght : 4.51 pm

Broadly lenl lculate

Basal cushion promlnent

h t s r - s o l n a l area tuberculale

tnler-splnal area punctata

Inter-splnal area granulose

Inler-splnal area pranulale

Splne he lght : 5.4 pm

Splne he lght : 6.8 pm

Splne helght : 3.17 pm

Splne he lght ! 4.72 g&

Basal curhlon not d l l f e rcn l la led

Inter-=plnal nrea rugulate

In ler -sp ina l area scabrale

lnter-splnal area granuhlc

Solne he lqht : 3.76 pm

Splne h e l g h l ! 5.85 pm ,

Splne he lqh l : 1.90 prn

Exlne thlckness ! 3.9 pm

Exlne 'thlckness : 0.32 pm

~ u m b - b i l l shooed

Basal cushlon promlnent

Splne he lgh l : 4.7 pm

Splne he lgh l : 5.94 pm

Splne he lqht ! 7.05 pm

Bass1 eushlen no1 d l f fe rcn l l s led

Inter-splnal area granulate

Splne he lgh l : 5.41 ym

Splne he lgh l : 7 pm

Exlne lh l ckne ls ! 13.63 gm

Exlne lh l ckner r : 12.33 pm

Parthenlum hys le rophoru l L.

Spllrmthes ul lglnosa Sw.

Lagarcea mol l l s Cav.

Montansa b lp lnna t l f l da C. Koch

Dahl la plnnata Cav.

Synedrella nodl f lora L. Caerlner

blplnnalus Cav.

Acanthospsrmum h l r p l d u m DC.

Hellanthus l a e t i f l a r t ~ a Pers.

Rudbcckla laclnl.te L.

Slgesbeckla or lenta l ls L.

Elevlhersnthern rudera l l s ISwar l r lSch.

Xanlhlum J. Koenlg

Ec l lp la p r o s l r s l a IL.1 L. Manl.

W* t r l l oba ta 1L.I AS. I l lh.

Spllanthes DC.

W* chlnensls (Osbeck) Merr.

l l t h o n l a ra tundl fo l la Blake

Clossocerdla bosvallea 1L.f.) DC.

Culzol la abysslnlca IL.f.1 Casr.

Tl lhonla d l v e r s l f o l l a (Hemsley1 A. Gray - -

Casinos sulphureus Cav.

Sub lentlculate

Bass1 cushlon promlnent

Basal cushlon slightly formed

Inter-splnal area punclate

Inter-splnal area smooth

Cralns 3.9-zonocolporate

Dumb-bell shaped

Narrowly Icnl lculate

Basal cushlon lnnnsplcuous

Basal curhlon promlnent

Inter-splnal area reticulate

Inter - rp lna l area m l l d l y granulala

Broadly lent lculate

Basal cushlon promlnent

In ter - rp lna l area granulate

Splne he lght : 5.71 pm

Splne he lgh t : 1.70 pm

Splne h e l g h l ! 7.29 gm

Cralns I-zonocolporate

Dumb-bell shaped

Sub-lentlculate

Gralns morphologlcal lv two d lss lm l la r types

Splnulate and tuberculate

Splnulate and splnate .

C o r e ~ p s I s grandl f lora Hogg.

Melampodlum paludosum B.H. K.

Zinnla elspanr Jscq. -

Cosmos caudatus Kunth --

Spllanthes H.B. K.

Spllanlhes olerscea L.

Spllanthes Jacq.

B la lnv l l l ea acmella L. Phl l lpson

Bldens h u m i l l r H.B. K.

Bldens p l losa L.

D.hlla Imparlallm Roeal.

T r ldsx procumbeus L.

Zinnla I lnear ls Benth. -- Callnsoga parv l f l o ra Cav.

Scanning e lectron micrograph o f t h e achene o f Calinsoga p a r v i f l o r a

Cav. ( X 1 0 0 0 ) .

7, DIVERSITY I N ACHENE MORPHOLOGY AND ITS

TAXONOMIC IMPORTANCE

The morpho logy o f seeds furn ishes va luab le da ta f o r

formulat ing t h e sys temat ic and evo lu t ionary concepts i n

angiosperms. The ev idences inc lude data f rom s i z e , shape o f

seeds and scu lp tu r i ng o f seed coats (Davis and Heywood, 1963;

Harpe r e t al., 1970). - -

The development and s t ruc ture o f seeds and f r u i t s i n

Compositae have been s t u d i e d i n var ious t r i b e s such as lnuleae,

E u ~ a t o r i e a e , Helenieae and L igu I i f e rae (Pandey 1976; Pandey - e t

al., 1982: Pandey and Singh, 1983; Gurucharansingh e t al., 1972). - - - Recently, a new c lass i f i ca t i on f o r Hel iantheae has been oroposed

b y Robinson (1981) based on t h e m o r ~ h o I o g i c a I charac ters o f

achene. His observa t ions were main ly based on l i g h t m i c r o s c o ~ i c

studies. In t h e present inves t iga t ion . f r u i t s o f 40 taxa belonging

t o 26 genera have been s t u d i e d in t h e l i g h t o f b o t h LM and

SEM. SEM s tud ies on t h e achene w a l l have p r o v e d to b e a good

taxonomic tool f o r d e l i m i t i n g t h e taxa, b o t h a t gener ic and

species l eve l .

On t h e bas i s o f t h e fact t ha t h i l u m ("attachment p o i n t " )

i s t he po in t o f attachment o f t h e seed to t h e mother p lant , it

shou ld b e considered as most conse rva t i ve s t r u c t u r e o f p r i m a r y

value. The sur face ornamentation i s n e x t i n t h e o r d e r o f

importance.

The pos i t i on and shape o f at tachment p o i n t v a r y w i t h

taxa. It i s marginal i n two taxa under s tudy , Lagascea mo l l i s

Cav. and Melampodium paludosum B.H. K.. It i s ob l i que l y

o r i e n t e d a t t h e p r o x i m a l end i n t a x a l i k e Eleutheranthera

r u d e r a l i s (Swar tz ) Sch., Hel ianthus annuus L., H, l ae t i f lo rus

Pers., S igesbeckia o r i en ta l i s L., Sp i lan thes c a l v a DC., - 5.

oleracea L., S, ul ig inosa Sw., T i t hon ia d i v e r s i f o l i a (Hemsley) A.

Gray, T, r o t u n d i f o l i a Blake, and Wedel ia ch inens i s (Osbeck)

Merr. . I n t h e r e s t o f the genera attachment p o i n t i s basal and la-

longate.

Heywood (1969) suggests t h a t scanning electron

m ic rog raohs o f seeds w i l l become a rou t i ne technique i n future fo r

f u r n i s h i n g ' in format ion on seed morpho logy . T h i s i s we l l

e x e m p l i f i e d th rough the pub l i ca t i ons o f Henr ickson & Hilsenbeck

(1979); Baden (1981); Ba rke r (1986); He d r e n (1987,. 1988, 1989);

Graham (1988); Daniel (1990) and Kelbessa (1990). Studies on

mic romorpho loy ica l characters have shown t h a t in te rpre ta t ion o f

cha rac te rs based on LM alone may b e i n c o r r e c t o r completely

lack ing, s i m p l y because t h e L4l does no t make ce r ta in features

prominent o r even not iceable. Semple and Semple, 1977; Kyhos - et

al., 1981; Stuessy e t al., 1973; have p r o v e d t h a t u l t ras t ruc tura l - -- features a r e genet ica l l y con t ro l l ed and hence can be used as a

taxonomic c r i t e r i a .

In t h e present s tudy t h e m ic ro -scu lp tu re o f t h e f r u i t wa l l

shows cons ide rab le d i v e r s i t y . The sur face p a t t e r n i s constant f o r

a species b u t may v a r y cons ide rab l y w i t h i n t h e genera.

Eventhough t h e achene surface i s s t r i a t e i n most o f t h e taxa, t h e

u l t r a s t r u c t u r e o f t h e s t r i a e d i f f e r s i n d i f f e r e n t taxa. Robinson

(1981) has p o i n t e d out t h a t achene w a l l i s s t r i a t e i n Melampodiinae

and Ec l i p t i nae . Bu t t h e present observa t ion r e v e a l s t h a t achene

w a l l i s r e t i c u l o i d i n E c l i p t a p r o s t r a t a (L. ) L . Mant. and re t icu la te

i n Melampodium paludosum B .H. K.. The sur face o f Parthenium

hys te rophorous L., Spi lanthes c i l i a t a H.B. K., 5. radicans

Jacq., and Synedre l l a n o d i f l o r a (L.) Caertner i s re t i cu la te . Rough

sur face i s n o t i c e d i n Bidens pilosa L., where as i t i s mammilate i n

Cosmos b i p i n n a t u s Cav.. Cranular sur face i s no t i ced i n Clossogyne

b i d e n s (Retz.) . The surface i s h i g h l y pubescent i n T r i dax

procumbens L.. . The sys temat ic s igni f icance o f seed shape i s recognised b y

Nees (1847); Bremekamp (1953, 1965) and C l a r k e (1901). The

d i f f e r e n t achene shaaes such as oblong. e l l i p t i c , oblanceolate,

cuneate, obovate, c y l i n d r i c a l and t u r b i n a t e a r e met w i t h i n d i f f e r e n t

t a x a under s tudy .

F r u i t co lou r a lso shows a w i d e range v iz . , ye l low, golden

brown, l i g h t brown, deep brown and b lack . The f r u i t colour i s

constant w i t h i n t h e t r i b e o r w i t h i n t h e genera.

The morphology o f t h e pappus va r ies g r e a t l y i n t h e t r i b e

mak ing i t useful i n i den t i f i ca t i on . The pappus i s w i d e l y accepted

as remnant o f t he ca l yx , and Cronqu is t (1955) assumed t h a t t h e

more c a l y x l i ke , 5-awned, squamose forms were p r i m i t i v e i n t h e

fam i l y . According t o Robinson (1981) i n advanced taxa the number

o f awns are reduced w i t h awns l i m i t e d to pos i t i on ove r t h e main

ve ins o f t he achene.

W i th in t h e t r i be , pappus t y p e s v a r y , f r om t h e epappose

forms t o h i g h l y spec ia l i sed paleaceous forms. Pappus i s cup - l i ke

i n t axa v iz . , Lagascea m o l l i s Cav., Wedelia ch inensis (Osbeck)

Merr . , - W. t r i l o b a t a (L.) AS. H i th . , Dah l ia p innata Cav.. I n

Par thenium hys terophorus L. pappus i s mod i f i ed as smal l scales.

B r i s t l e l i k e pappus i s n o t i c e d i n Acanthospermum Shrank., Zinnia

I i n e a r i s Benth., B idens L., Cosmos Cav., Glossocardia Cass.,

Guizot ia Cass., Synedrel la Gaertn., Spi lanthes c i l i a t a H.B. K., 5.

oleracea L., 5. ul ig inosa Sw., T i t hon ia ro tund i fo l i a Blake, - T.

d i v e r s i f o l i a (Hemsley) A. Gray. Epappose achenes are observed i n

t axa such as Xanthium L., Melampodium L., Hel ianthus L., Montanoa

b i p i n n a t i f i d a C. Koch , Rudbeck ia L., Spi lanthes - calva DC., Dah l i a

Cav., and Guizot ia Cass.. Pappus i s h i g h l y spec ia l i sed paleaceous

t y p e i n Galinsoga Ruiz. & Pav.. I n Tr idaxL., pappus i s setose.

It may be noted t h a t b o t h T r i d a x L. and Galinsoga Ruiz. & Pav. a r e

t r e a t e d as advanced b y many researchers (De Candolle, 1836;

Bentham, 1873; Bentham & Hooker, 1876; Hoffmann, 1890; Stuessy,

1977; Robinson, 1981).

F r u i t s i z e cons iderab ly v a r i e s i n t h e t r i b e . Corner

(1976) remarks t h a t p r i m i t i v e angiosperm seeds a r e o f medium size,

f rom w h i c h smal l and la rge seeds a r e d e r i v e d . The v i e w i s we l l

accepted b y t h e contemporary bo tan is ts I i k e Takhta jan (1980).

However, Corner (1.c.) -- f u r t h e r ind ica tes t h a t no l i v i n g seed i s

e n t i r e l y p r i m i t i v e and t h e characters may v a r y w i t h fami ly . In

t h e taxa s tud ied t h e f r u i t s ize v a r i e s f rom a minimum o f 1.49 mm

(Sp i lan thes u l i g inosa Sw.) to a maximum o f 19.02 (Cosmos

sulphureus Cav.). Compara t ive ly . l a r g e r f r u i t s a r e observed i n

taxa coming under t h e s u b t r i b e Coreopsideae. The u r t i c l e o f

Xanthium indicuin J. Koenig i s 17.5 mm long. SmaI l e r f r u i t s a re

observed i n Par thenium hys terophorus L., Gal insoga p a r v i f l o r a

Cav., and T r i d a x procumbens L., a cha rac te r ass igned t o advanced

taxa (Corner I .c. 1 . It i s noteworthy, t h a t a l l these taxa a r e -- t r e a t e d as advanced b y many workers. (De Candolle, 1836; . Bentham, 1873; Bentham & Hooker, 1876; Hoffmann, 1890; Stuessy,

1977; Robinson, 1981). . Medium s i z e d f r u i t s a r e not iced i n t he

members o f Verbesineae, and i n taxa l i k e Acanthospermum h isp idum

DC., and M e l a m ~ o d i u m paludosum B.H. K..

The r o l e o f achene morphological s tud ies i n systematics

w i l l b e d iscussed l a te r .