TIIE GENETICS OF TROPA.EOLUM .MAJUS. II

BY E I L E E N SUTTON

Joh~ Innes tto,rticultu~'ql Institugon, Merton

(With One Text-figure)

]'. INTI~ODUCTION

S~NCE Dr 3{offett lel% this Ins~itution in 1935 I have carried on his work on die genetics of f~'oTaeo~u~n majus. The present paper is a supplement ~o the earlier res~flts published by Noffett (1936).

In 1936 two fm'ther papers on Tropaeolum were published by other workers (Eyster & Burpee; Whaley & French). Reference to some of ihefr results will be made in later sections of this paper.

2. 8~¢L~.-FACTOa R~TIOS

The factor N

The recessive factor n has hitherto been found only in plants of the Compact, bushy habit (hh), and its effect on the BB type with spreading rnnners is not yet known, h b n n plants are extreme dwarfs with a diameter of 5-10 in., whereas b h N N plants have a diameter of 1 R. or more. The gene n also reduces the size of the leaves, but not of the flowers; and though the pollen i; functional, the anthers fail to dehisce.

t?~ ratios for this factor are given in Table I.

TABLE I

F~m/ly N n TotM 20/35 50 18 68 48/35 71 27 98 49/35 43 16 59 5O/35 59 14 73 32/36 18 5 23 38/36 91 24 ll5 31/37 i0 3 13 32-137 15 3 1 g 43/38 60 22 82

Total: Ob6. 417 132 5-£9 Exp. 411-75 137.25

ft~e factog" M

The effects of ~bhis factor are on].y seen in flowers wRh anthooyanin pigments (determined by the general a,~thocyanin factor A). In. the homozygous recessive condition (ram) this gene produces a metallic

go~rn, of Genetics x x x v i i ; 11

162 The -~e.net'tc.s of T r o p a e o l u m m a j u s

sheen on the petals and a ceil-sap 2H value which is slightly but con~ s[stently Ifigher tha.n ia the petals of NIM plants (5.9-6.6 instead of 5-5-5.9; see Table Xt).

ACIV[NI scarier ./kcRMNI bright deep

red AcrMNI pink

Its effects upon flower colours are as follows:

ACMm scarlet ACn-lm bisoui~ AcRMm dull red A c R m m mauve or

b / :0Wn

AerlVlm pale pink A c r m m pale mauve

A c R m m plants have mauve flowers when the plastid background is primrose, and brown flowers when the background is yellow. This geno- type quite likely corresponds to Rasmuson's "lilafarbigen Pflanz" of which he writes (1920): "Die Farbe ~ird bier fiberall 'lila' gemannt obgleiGh sic bei dunkelgelben Pflanzen mehr braun, yon einer eigeatiim- Iiohsn Nuance, war."

The flowering sea,sm~ in m m plants finishes some weeks before that of MM plants, and the leaves also begin to yellow relatively early.

2[aries for ~ke gene M in the combinations AcR and Acr, giving c[isfiinguishable l~eterozygofles, are given in Table II,

TABLE II (a) Backcross~a, ~ xlVIrn

F~mfly ~ Nlm 26/36 33 48 27/36 16 2.1

To~M: Obs. 49 69 Exp, 59 59

(b) F~'s, ~ ~Mfed

28/36 9 14 9 2.9/36 4 iI 3 30/36 3 6 3 31/36 7 16 9 34/36 14 19 I5 30/37 4 I0 6

Tol;ah Obs. 41 76 45 Exp. 40-5 81,0 40,5

The.factor" T

,TobM 81 37

118

To~M 32 I8 12 32 48 20

162

Antkocyanin. producti.on fll ~he petals is partially inlHbited by tke factor t, and flowerocolours are afl'ected iu the following way:

ACTT scarlet AQTt scar].et ACtt salmon Act lTT deep red AoRTt paler red Actl t t tinged AcrTT pink AcrTt yellowish pink Acr t t tinged

AcRtt and Acrt t plants have only a ~ransitory tinge of co]our in the flower buds, with an oceasionM slight .flush in the expanded ps~als. The

E~L~EN SUTTON ] 63

colour is so much reduced in both genotypes that they are only distin- guishable fl, om one aa~other by the honey g~fides, wSJch are dark red ill AcRtt ~md pink in Acrtt plaints. The 2~}I vat~e in the celt sap of the petals of these plan+os is as high a.s it is in acyanio (an) flowers (6.4-6.8) and the e:ffect is probably comp.'-~rable to that found by Scott-Noncrieff (1936) in P~i~nda, si~ensi~ plan~s ca:crying the gene R for acid cell s~p, where the I)H of acya:lfic corolla tubes was higher than that of pigmented corolla tubes.

Single factor ratios for T are given in Table IIi .

TABLE Ill

(a,) T t self , d, F2's Family T t To~I

14/32 10 4 14 4/33 ~.1 6 47 1/3~ 55 11 66

28/37 33 II 4~: To~1: Obs. 139 32 171

Exp. 128.25 42.75

(b) T~ × TT, baekcrosses

Family T T T% To~M

28/37 9 6 15 To~,%l: e t a . E2 59 I11

Exp. ~E.5 6~,5

(~) T t × it,, b~ckcross

~ m i l y Tt t t T o ~ t 4/34 3'/ 30 67

t~xp, 33,5 33.5

The factor L

The factor L which localizes the anthooyalfin pigment in a spot, at the base of She petal, was mentioned by Moffett (193G). This effect is im completely dominant, and the hetez'ozygotes can be distinguished be- cause the oolour tends to spread, to a greater or less extent, towards the

edge of the petal; whereas in the homozygotes I have fonnd the eolour to be confined to a small spot. The difference between komozygote and heterozygote is shown in the photograph (Fig. I).

l-iefieroz)~ofies may bear flowers wi~h a d~sdnct spot and ~owers with considerable pigmentation in the outer part of the petals, but at any one time one of these types is predominant, and the degree of pigmen%a,- Non seems to be influenced by environmental factm's, as stated by Whaley & French (1936). In scarlet (C) flowers heterozygous for L the spot is always of the more spreading type.

11-2

164 Tk.e 6:e~,e~.ic,s qf Tropg~eolum majus

• .'<:

• . . . . . . . . " .

:....

• .

.'~ >..

// ,:o

8® ~ Z

g ~

• ~ .o

,.-<~

4~ 0

~2

hO . ~ ,.W

2~

bO hfl

N & ,

EILEEN SUTTON 165

The following ratios have been obt, ained for this gene (Table IV).

TABLE IV {c 0 l re ' s , L 1 sMfed

:Family L I To~al 46/38 79 32 111

Exp. $8"25 27.76 (b) Baeke,:ossea. LI x 11

32/38 26 30 56 34/38 6S ¢9 I 17

%'oral : Ohm 9"[ 79 17a Exp. 8b,5 86-5

These results agree with l%asmuson's conclusion th.at a dominant gene determines the spot (1920).

There is evidence, however, tha t two genes in different loci are necessary in order to localize tlle eel.oar.

A cross was made between Sutton's variety " Cloth of C~old" (yellow aoyanic flower) and a pink4iowered line (Acr, 21-"/32). The P1 fi'om this .cross had ~.owers with spreading scarlet spots: and R might be supposed tha~ the spot factor as welt as the scarlet factor was introduced ttn'ough "Cloth of Gold ", in which it bud no phenotypic expression owing to the absence of any anthocymdn pigment. However, this same variety "Cloth of Gold", when crossed with another variety "The l~ing" (soarlefi-flowered, AC) gave both F~ and Ez with no spot,. I t therefore. seems z'easonable to suppose that both "Cloth of Gold" and the pink- flowered plant (21~-/32) carried only one of two genes necessary for the spot character.

I t may be assumed tliat "Cloth of g o l d " carried the gene L and the pink st, ock carried a second gene for spot. designated by K, so that the /v I had the constitution KkL1. tn eon~rmation of this, the _~, (25/33) when selfed gave an _P~ (40/34) of 27 plants !with spot and 96 without, together with 7 acyanie plants. The ratio of 27 : 26 in the cyanic (A) class does not deviate significantly from a 9 7 ratio for two complementary factors (X~-=0-6065; ~).~.=1; P=0-50-0-30).

On baokcrossing to a KKll plant, equal numbers of the four classes XKL1, KkL1, KKtl, and Kkll should be obtained, and as the ftrst two classes have both. dominants for spot and the last two classes have only one, this should give a ratio of one spot: one no spot. On backerossing the F 1 (25/33) with the pink P~I stock (17/33), assumed to have the con- sti.i, ution KI411, a family (39/34) of 6,3 plants was obtained giving the ratio of 27 with spot : 41 without. This is within the limits of random deviation from a 1 : 1 ratio (X2=2.8824; D.F. =1 ; P=0-I0-0 '05) .

166 Tire go,notice of T r o p a e o l u m m a j u s

Two families obtained by selflng spo[ plan[s in 39/34 gave ratios approximating to 9 :7 (expected from KkL1) while two families gave ratios approximating to g : 1 (expected from ]<KL1).

The data-given by the cyanic :plants in all these families are included iu Table V.

TABLE V O b s e r v e d E x p e c t e d

S u p p o s e d gene~ie r a t i o s r a t i o s c o n s t i t u t i o n spo~ : no s p o t : no

F a m i l y P a r e n t s o f p a r e n t s spo~ s p o t T o t a l

20/33 *'The IGng" x kkll × kkLL -: 3 -: 3 " C l o t h of G o l d "

30/34 20a/33 selfed k k L i - : 28 - : 28 28 25/33 " C l o t h of Gold" × k k L L x tf. .Kll 25 ; - 25 : - 25

21~/32 40/34~ 25~/33 seKed IEk.L1 "?7 : 26 30 : 23 53 39/34 25 ~ x I76/33 K k L t x K_Kll 27 : 4~1 34. : 3.i 68 g8 /35 39~a/3A sel fed K k L 1 36 : 34~ 39 : 3 I 70 52/35 3 9 ~ / 3 4 selfed K k L 1 41 : 27 38 : 30 88 49/35 3 9 ~ / 3 4 so(fed KK.L1 37 : 6 32 : t l 43 50/35 391s/34 selfed KK.LI 43 : 9 39 : 13 52

T]ze factor B Two 1938 families gave very abnormal ratios for the a]lelomorphs

B, b, determining creeping and bushy habit respectively. Family 31/38 came from the backcross 5~x a&/37 (hxar x BbXx

Aatlr) . A ratio of 39 B : 18 b was obtained, which deviates significantly from I : 1 (X ~ =7.7368; ~.~. =1; P = < 0.0t). The factor i t which is linked with B (see next section) gave a ratio of 19: 8, which is also badly out (X2=4.4815; ~.~.=I; / )=0-05-0.02) , while the ratios for X (33: 24) and A (27: 30) were reasonably good. The fifty-seven plants ix~ this family cams fYom seventy seeds; nine seeds failed to germinate and four pianos died before scoring.

A reciprocal cross (389x 5~/37) gave good ratios in family 32/;8 for all four fa,cters, B (2.2 : 34), X (29 : :27), A (27 " 29), and R (1i : 16).

Family 51/38 was ala f~ obtained by selfing 38~/37, a sister pla.ug of • 38 ~, also of the constitution BhXxAat l r . The ratio :Nr B was % : 2 5 (X~=17.693; D.F.=t ; P = <0.01), while the ratios for X (g5: t4), A (37 : 12) and R (28 : ].1) were good : the slight e:~eess of r is not significant. In this family only one out of 50 seeds failed be germinate, and every plant was scored.

A ~h:ird sister' plaut (38a/37) gave two 19,38 families w~ th normal, ratios, One of these, family .30/38, of which 38 a was t]?e male parent, gave good backoross :ca,tics :for B (36 : 4:2), X (36 : ,i2) and R (2~[ : 33); the female parent u~as also heterozygous for A, and the ratio 'for this gone was

EILEEN SUTTON 167

57: 19. The ethel' family, 50/38, came from sol.ring 38a/37 and gave reasonable I~'~ ratios for the four factors (B 41 : 14, X 39 : 16, A 45 : S, R 37 : 8).

The pedigree of family 38/37 is as follows, tn 193'1-the cross ~11~ x 3825 (BXACR x bxacr) was mad% giving the 1935 f 1 family 56/35. One plant of this family was selfed, and in the -Y,,. (36/36) of 86 plants the ratiOS for B, X, A, C and IR were good (see Table VI). 36a'V36 (a plant of genetic constitution BbXXAAcelRr) was now crossed to 6'~/36 (bxacr) and the progeny grown in family 38/37 gave the ratio of 8 : 6 for both the genes B and 1% Three of the Bt l plants (38 a, 3g ~;, and 339) were used for backerossing and soiling, with the results recorded at the beginning of this section.

These results can be e~plained by ]?ostnlathlg a gone which adversely affects the male gametic or gametophytic stage only, and which is in the same chromosome as the gene B. This gone may, for instance, greatly retard the pollen-tube growth, of grains carrying it as compared with that of grains carrying the normal allelomorph. As it must act in the haploid phase it cannot be considered either dominant or recessive with regard to this effect, but it may be designated as g, the normal allelomorph Being G.

A GB/gb plant will have four eqnally functional classes of female gametes, , the non-crossover types GB and gb and the crossover types Gb and gB. In the pollen two of these classes, gB and gb, will Joe handi- capped by carrying ft. As the crossover class gB is relatively small, the effect will be to eliminate from competition a relatively large ~umber of male gametes carrying 5, so that the zygotic ratio of B : b will show a detlciency of recessives. The expected F~ ratio B : b (assuming tha t no male gametes carrying g effect fertilization) will be (2 -2 ) : 2, where p is the crossover value for GB. Therefore the closer the linkage (i.e. the smaller the value of 2), the greater will be the excess of B over b plants.

I f a GB/g~b plant is used as female in a backeross to a Gh/G5 plant, the ratios should be normal, as the female gametes are not differentially affected by g; but if t]he GB/gb plant is used as male parent there will be a deficiency of b gametes and bb offspring, as in the self, and the zygotic ratio expected for B : 5 is (1~2) : 2 - - t h a t is, the same as the ratio of non-cross-overs (GB) to cross-overs (Gb). This kind of result was found in the reciprocal crosses made with 38~/37: used as female the ratio B : b was quite good (family 32/38) but used as male it gave a defie.ieney of b (family 31./38).

A gB/Gb plant will when selfed give a deficiency of t~ plants. The

168 The Ge'~e~ic~ qf T r o p a e o l u m m a j u s

expected, ratio will be (1 +20) B : (1 -~ ) b. Again, the closer the linkage, the greaeer the excess of one el.ass. The /< ratio of 24 B : 25 ]a in family 5]/38 shows that the parent 38~/37 had due constitution gB/Gb aecord~ ing ~o the hxpothesis.

38~/37, which gave good ratios when soiled and when used as male parent i~ a baekcross, was presumably homozygous for the normal a I l d o m o r p h ( G G ) .

The pollen of many plants in 1938 families was examined. In T'ro- peedum there is always a rather high proportion of empty pollen grains (10-50 °/o ) and there was no detectable difference betwee~ plaz~ts in the families with abnormal ratios and those in a wide range of ot~er families. R would seem, ~herefore, ~hat the s~.~bsequent behavionr (e.g.

Family 36/36 3 8 / 3 7

sofss 31/:~s 3-U3s sl/3s

TABLE VI

P a r e n t s Suplaosed c o n s t i t u t i o n e f p a r e n t s

561z135 selfed B b X _ x ~ a C o N r G G 36 a~ ;.: 6a/36 B i ~ X N c c l q r G g x b x a c r G 3 5 ~- :< 3 8 ~ j 3 7 bbx~xiarrGG x BbX.x-Nal~r GG 38r~/37 selfed 13hXx_g.al~rGUar 5 ~ × 38~/37 D x a r G × B B ~ - A a R r G g :18 ) x 5~/37 1 3 b X x _ & a R r G g x b x a r G 33s/37 selfed BbXzAaRrGg

R.atios F ~ "x

]B: :b X : x A : a C : a R : r T o t a l

6 6 : 2 0 6 2 : 2 4 6 7 : 1 9 5 1 : 1 6 12:1~t 86 8 : 6 - - - - - - 8 : 6 14

3 6 : 4 2 3 6 : 4 2 5 7 : 1 9 - - 2 4 : 3 3 78 4 1 : 1 4 3 9 : 1 6 4 5 : S - - 3 7 : S 55 3 9 : 1 8 3 3 : 2 ' 4 2 7 : 3 0 - - 1 9 : S 57 5 )2 :34 2 9 : 2 7 2 7 : 2 9 - - 1 1 : 1 6 56 2 4 : 2 5 3 5 : 14: 3 7 : 1 2 - - 2 6 : 1 i 49

pollen-tube growth) of pollen grains is affected rather than their viability at earIier sbages.

As the ratios in family 36/36 were normM, g~e gone could not have appeared earlier than the 1935 generation of this pedigree. I t mus~ in fact have arisen by mutation either at game~ogenesis in .56~s/35 or somatically in 36s'~/36, making this plant heterozygous (Gg), As it was used as female in the cross with (P/36 it gave normal ratios in ~amily 38/37, and owing to crossing-over between B and. G these geI~es were bod~ coupled and .repdled i~.1 differen~ plantsin this family.

(bossing~over between GB and between Gtt is of the order of 30- 40 %, and the linkages between these pairs of genes are not ~s strong as 12le BR linkage. L1 families 31 and 51/38 the ratios for B are more d~s~ turbed t.han those for R. The order of the three genes is probably GBtR.

3 . T W O - F A O T O : a ICAr:dO,.S

(a) Li,d~:a,qe

Apart from the hypothetical [i~fl~age of B and G, I have de[Lcitely estab[ish.ed a, linkage beewee~ B and R. _Ba,ckeross and .F~ ra~ios for these

E~LEEN SUTTON 169

factors in coupling ~ r e given in Table VII. l~amilies 31/38 and 51/38 are excluded on account of the abnormal ratios for B.

TABLE VII

Fa.mfly ] ~ ]~ r b R b r To hal 26/36 3,I- 3 8 36 8 i 38/37 8 - - --~ 6 14. 80/38 fi2 2 2 31 57 32/38 9 '2 2 14, 27 ; fa ta l 73 7 19 87 ]. 79

(b) P~'a 31/36 :t 9 -± S 4: 30 36/36 10 1 2 3 16 50/38 33 ~ 4: 8 45 TotM 62 5 9 15 91.

A combined estimation of d~cse families for ]inkage by die method of maximum likelihood gives a crossover value of 0.t25 +0-02.

The fi~ctor M may also lie in ~he same chromosome as B and R. Data for B and NI in repulsion do not deviate significan[ly from ~he numbers ex-pected on the assumption of i~dependen[ segregation; but. th.e data for R and IYi (also ill repulsion) axe nob in agreement ~ith this assumption (for backcl'osses, X ~ = 1.220; ~).m = 1 ; P = 0,30-0-20; for F~'s X"- = 8,385; D.F.=]; P: <0-01). The rados are given in Table VIII.

TABLE VIII

(a) Backcross %r B ~nd M

F a m i l y B M Bn~ blVi D m Tota l

28/36 12 25 23 21 81

~,xp, 20.25 20.25 20-25 20.25

(b) F,,'s for ]3 and ]VI

31/86 17 6 6 1 30

Exp. 16-875 5"G25 5'825 1-875

(c) ]~ackcrosse, s for R and XVI

F a m i l y PdVf X t n r M r n ~ Tota] 26/36 13 29 20 19 S l 27/36 9 9 7 12 37

To,a t : Obs. 22 38 27 31 118 Exp . 29-5 29.6 29.5 29-5

(d] F. ' s for a and M

31/36 17 5 6 2 30 3,1/3~ 21 15 12 -- 48 30/37 S 5 7 - - 20

Tota l : Obs, 46 25 25 2 9S Exp . 55-125 18-375 18-375 6.125

The radler me.~gre data. afforded by repulsion Ez's also suggest a linkage between Y (one of the leaf-oolour genes) and C (scarlet itower-

170 The Genetics of T r o p ~ e o l u m m a j u s

colour). The ~hree f~railies combined (see Tabie IX) give a X" value of (10-162; D,.F.=I; P= < 0"0I). On the other hand, the numbers are quite a good :fi~ for coraplete linkage.

TABLE IX

Fa-ulily YC Yc yC yc Total

20/35 I5 I0 13 - - 3~ 29/37 ii 5 ~ - - 20 3[-2/37 12 3 6 - - 21

Tot~h Obs. 38 18 23 - - 79 Exp. 44-i I@8 1t-8 4.9

( b ) I nde.pendent two-f ao: o~" ~eg~ egation

Since the pablicatioa of Moffett's data in 1936 further" families have been obtained wlfich establish the independence of the genes.B and A. The ratios for these and for other pairs of independent genes are included in Table X.

TABLE X (1) BBAa self, d. Y..'s

Family BA Ba hA ba Total

36/36 50 16 17 3 86 50/38 33 8 I2 - - 53

Torah Obs. 83 24 29 3 139 :Exp. 78.1875 26-0625 26.0625 8,6875

B b A a x b b a a , backcrosses

54/35 11 t0 12 18 51 32/38 I I i I 16 18 56

TotM; Obs, :?.2 91 ~8 36 107 ,Exp. 26,75 26.75 26.75 28-75

(2) B b X x selfed, F2's

tr~ mily BX B x b X b x " Toga.1 36/36 46 20 16 i 86 50/38 80 ] I 9 5 55

To~l: Ohs, 76 31 25 9 14-I Exp. 79.3Z25 26.4375 26.4375 8,8125

BbXx x ~ b x x , b~ckerosses

30/38 .[G 20 ] 9 22 77 3.2/38 13 19 16 18 66

Total: 0bs. 29 39 35 40 143 Exp. 35.75 35-75. 35.75 35.75

(3) X x & a sslf~d, Y.%

Family XA X a xA x a Tot~! 29/36 I2 7 5 - - 25 30/36 lO 2 3 1 16 33/:.16 32 12 10 3 .57 36/36 5[ I I [5 8 85 50/38 32 O 13 2 53 51/38 28 7 9 5 49

°t'o~al : Obs. [65 45 57 19 286 Exp, 160,875 53,625 53-625 17,875

EILEEN SUTTON 171

TABLE X (con~.)

2XxA a x x x a a , b~ekcroases

31/38 17 16 10 I4 57 • , ~ , 15 14 12 15 56 3.~138

Total: Obs. 3g :30 22 29 n a Exp. 28-25 28-25 28-25 28.25

(4) X x C c sailed, t,~'s

Family XC Xc x C xc Total 36/36 39 13 13 3 68

Exp. 8'8.25 19-75 12-75 4-~5

XxC c x xxcc , backcross

:75/37 13 7 18 10 48 Exp. 12 12 12 12

(5) XxRr self~d, l)~'s Family XR X r xR x r Total 36/36 10 3 2 1 16 ¢5/38 25 9 3 5 42 50/38 27 5 10 3 45 51/38 20 8 6 3 37

Total: 0bs. 82 25 21 12 1`40 Exp. 78.75 26-25 26.25 8-75

XxRr x xxrr, backerossas

30/38 t2 15 12 18 57 32/38 6 9 5 7 27 39/38 12 14 18 13 57

To~al : Oba, 30 38 35 38 141 Exp. 35'25 35.25 35~25 35'25

(6) A a Y y seligd, F~'B

Family AY A y aY asr Total 20/35 32 13 10 5 60 48/35 53 ]7 18 3 91 57/35 7 3 4 - - 14 59/35 38 9 10 2 59

Total: 0ha. 130 42 42 l0 22"4 Exp. 126 42 ~_2 I4

(7) V v A a selfed,/L's ]?~mily ~JA Va vA va Total

59/35 40 9 7 3 59 60/35 19 9 8 2 38

Total: Obs. 59 18 15 5 97 Exp. 54-5625 18,1875 18.1875 6-0625

~. ~I2fSIOLOG~ ~ OF DO'CTBLENESS

The description of the mol~photogy of double/lowers in. f'rol)aeolu~n m~ju,~' by Eyster & Burpee (1936) treated of two forms of doubleness, ~h.e "Golden Gleam" or semi~double and a super-double. Both of these forms are due to mutants of the same gene, the se~-double (d) being recessive to normal (D) while the super-double (D') is dominant.

172 The Ge'net.ica of T r o p a e o l u m m~¢jus

Although I have grown only the semi-double form and have made no attempt to study experimentally the physiological action of this series of allelomorphs, it seems worth while to re,dew wh~t is known of the gene effects in the light of @.o[dschmidt's theory of developmental rates.

The normal order of development of floral organs is ee,~tripetal-- calyx, coroIla, andraecium and then gynoeoium. Each whorl of organs develops by cell growth, cell division and further differentiation from a zone of the receptacle which has aIready been differentiated as the basis of one of these four categories. This initial differentiation may normally be eompIeted before ~he growth of the ~rst (outer) whorl begins, or differentiation and growth may proceed together serially from the outer to the inner whorl; bat before the growth of any particular whorl, such as the androeeium, begins, the tissue from which it develops must have been differentiated from the petaloid zone on the outside, otherwise an extra whorl of pega.]s would be formed instead of stamens.

tn the f'ropaeo[um s~zper double it appears that the normal time relationship between the processes of differentiation and growth is upset. The growth of the two inner whorls (stamens and carpels) is premature in relation to differentiation., or differentiation is retarded in relation to growth. Hence a difference from the preceding petaloid zone is not eomple~ed in the staminoid zone before the growth of the organs begins, and these organs have a markedly petatoid character, although alley are partially differentiated and can form anthers and pollen. The same occurs in the developmen.t of ~he innermost (pistilloid) zone, which, is also petaloid and does not produce ovules which can be fertilized.

The incomplete differentiation of floral organs is only one of the effects of the gene D'. The second and equally marked effect is the multi- plication of growing-points. The snper~doubIe i].o~rer has, according to Eyster and Burper, for~y to fifty petals, about thirty petaloid, stamens, and about 50 petaloid earpeIs--a total of over one htmdred iloral parts as compared with ~wenty-one in the normal flower.

These two effects can both be seen in the seminal.cubic in lesser degree. The petaloidy extends only partially to the stamens, most of which are normal, and not at all ~o the carpals. Proliferation of pa.rts occurs in the petal, seamen and e.ar.pel zones, but far less {hart in the an}per-double. Eyster's average ~gures are: pets Jr 9-88, stamens 11-94, carpels 3-8< instead of l~ve, eight, and. three in the single flower. From a co[rag of twentydive flowers from different pla~ts in 1938 1 obtained the averages: petals 7.36, sfiamens t2.4:8, carpels 3.¢8.

Neither form of double exceeds the normal sepal number of ~lve. The

.~ILEEN SUTTOh r 173

fact that normal differentiation and growth occurs only in the calyx zone suggests that growth immediateIy follows different, iation in each zone, rather than that the four zones are all differentiated before growth begins in the outermost. The effects of the allelomorphic mutants of 1) differ only quantitatively, in the relative :rates at which, after the sepal a~c:.ge are formed and before differentiation of the staminoid and pistilloid zones is complete, th W cause the proliferation of petMoid grovdng-points.

In the semi-doubles, flowering is delayed until one or two weeks after that of singles begins, and the first flowers of dd plants are usually single, with. the normal nuraber of floral parts. These differences s~ggsst that in the early stages semi-doulJle plants have a retarded floral development (whether normM or a}mormat) compared with singles or supe>doubles.

5. BIoem~is'n,,Y o~ ~ ~ ,ow~. ¢OLOm'~S

A#~.thowe~{ns

The resuRs of preliminary work on the fiower-colour pig'men% have been mentioned by i~offett (1936). These results indicated t~at both the scarlet and pink eolours were due to an anthocyanin derived from

1 " r " pelargonidin, while the deep red was clue to a aernattve of cyanidin. Since that time, however, several AcR (deep red) and k c r (pink) geno- types have been investigated, and it has been found that both these genotypes contain mixtures of eyanidin and delphinidin derivatives in varying proportions. There is a. marked variation of colour reactions in between the limits of pure cyanidin and pure delphinidin.

The pigments in the petals are not necessarily the same as those which occur in other parts. Robinson & l~obinson (1932) found that one.variety, "Empress of India". contained pelargonidin-3-biodde in the petals: eyanidi>g-bioside in the sepals and delpNnidin diglyeoside in the leaves.

The sugar-type of the petargoniclin pigments has Mways been found to be 8-bioside. ]In flowers with eyanidha-delphinidin mixtures, and those in which cyamdin derivatives predominate, the sugar occurs fll the 3- bioside form (Robinson, 195t, 1932), and it is probable that the del- phi~fidin t~-pe pigment. (predominant. in mauve flowers) is similar. In {he variety " ~ g Theodore", however, the R,obmsons found delphinidin 3-5-diglyc.oside. Sugar types in the anthoeyanin pigments of plants are discussed by Lawrence el. d. (in {he press).

Flc~vo~e

All flowers examined coe~Mned a. large a, mount of flavone. Those which were separated into lined and unlined petals showed that the lined

174 The Ge)'rekics of T r o p a e o l u m m a j u s

pefals contained much more fJ.a, vone than ~be unlined. There is Lhus a concentration of both pigmen.~s in the lined petals (possibly in tim litaes themselves).

?l-i veh~es A ~able of pH values for rite petal cell-sap recorded by Miss Scott

Moderieff and Ivlr Prise is given below (Table XI).

TABLE XI

Unpigmen~ed 12/35, i~H. 6.30

Pigmeri~ed

Low pH Hfigh 2 I t A e r M T 23"-/37 p}I 5-83 A c r l ~ r n T 31~1/36 io7=~ 8-00

10~/37 5'38 AcrrnrnT 35i/37 6"61 21~/37 5,64 AcrMTt 20~/36 5.89 28zT/37 5-87 233/37 6-06

28-;~/37 6.08 AerMtt 28~u/37 6"80

283s/37 6-40 AcI~dVIT 33'~'~/36 5.91 A¢l:l!VIxnT 3P"-/36 6.10

23~:/37 5'81 A cE~'xma T 2i/37 6-11 34i/37 5"50 AcI~2~2T t 20r'/36 6-00 34:/37 5"82 23~/37 6'01

AcPdVItt 28~a/37 6-64 AC1PIT 291a/37 5"58 A g m m T 29i~/37 5-92 ( IVEVI or 29t~/37 5"76 iVlrn) 29~7/37 5.70

292:/37 5'66 A C M t t 14/36 .5.69

1~/37 5-70

6. DISCUssioN

Two aspects of the data on T'ropa.eoh~.m sv@l;8 collected by different workers deserve special eonsicleration--the effects of the gone C a~t the occurrence of pairs of gents affecting the same character.

In the presence of the general an~hoeyanin factor A, the gone G is responsible for the production of aathocyanins derived, h'om pelargonJdin. This type of pigmentation is usually a recessive mutant character in cultivated plants, but it also occurs in wild types as a dominant and i% seems reason.able to suppose ~hat the gone C in T~'opaeo~um is ~ wild-t?Te dominant. I have been unable ~o obtain any i~ormation, about the pkenotypie characters of the wild type, whielh is a native of Peru and nsighbourmg South Amerioa~l countries and was introduced it72o cult:ha- l;ion in 1684. The iuteracbion of C with o~her genes is interesting. r is a specific modifier of ec, but ACtl and ACr plants a,re indistinguishable. In. co pla.~tts Mirx and Tt are i.ntermediage, the genes M and[ T being in- completely dominant, while in. the presence of C, M m and Tg plants cannot be distinguished h'om the homozygous dominants MM and TT.

EIzESN S ~ T O N 175

On the other hand, CL1 plants alw~o~s have a spre~ding spot and resemble 6he fall°coloured 11 recessive more than eL1 plants, which may have flowers which are nearer to the dominan~ LL.

All these modifiers are therefore much less efl:ee~ive in GG tha,n i~z cc

pla,nbs. AbogeCher some twenty dif£ere].zt genes l~ave been identified in

Tropceol~m- m.a~'~ts, and eight of these are i~eluded in four pairs of com- plemeuta,ry or polymeric factors. The gene pairs P, Q and K, L are stricJy eompleme.n.~ary. The other two geae pairs are the ]eaf~eolour genes X, 27 and the ~wo gm:es L, U for leaf-shape described by Whaley & French (1936). Their gene L is not the same as Noi%i,t's gene L for loeaI- ized flower coIour, but olze of their ge~.es (L or U) is probably identical with Bateson's gene I for ivy-leaf (Moffett, 193@

Tbds grouping of more than one third of the known genes i~z pairs is rather striking, and as several workers have found the hc~2bid chromo- some number of reduced Tro2)aeo[um .mains to be ].t (Gaiser, 1930), this phenome]~on may be due to tetraploidy. Pairs of similar genes which were l~ot allellomorphic n~ght be found in nit]let an allopol)~plbid or an autopolyploid. In an allopolyptoid this would resuit from chromosome doubling following the hybridization of two closely related species wNoh were nevertheless slightly differentiated from one another in gene structure. In an autolaolyploid ig would be necessary ~ao postulate con- siderab[e differentiation of~he two sets of chromosomes after chromosome doubling had occurred; otherwise the potyploid would give tetraploid ratios instead of diploid.

The results obtained for Trop~eoZ~n nz@~,s are not u~ike those recorded by many workers on the potato (summarized by Crane & Lawrence, 19.3t, pp. 89-I02) in which different degrees of polyploidy undoubtedly occur.

The partial sterility affecting both pollen and ovules (in 1985 esti- mates of ~he percentage of seeds set by different plants ranged from 1S- 39 %) might also be due either to allo- or au~opolyploidy.

However, Sugiura (1925) found that the cl~omosomes pair normally at first meeaphase of meiosis, and the suggestion of polyploidy must be considered merely speculative, even if highly probable.

7. S u ~ B : ~

1. A description is given of the inherita.nee and effects in T.;opaeo~m re@us of three new genes (N, M, T), of the genes K and. L, and of a factor causing ab~orma] ratios for the geue B.

1+76 ~V~e (~e~etic,~ of T r o p a e o l n m m a j u s

2. The results of two-factor segregations are tabulated. • 3. The physiology of two forms of gene~ic doubleness is discussed. :I~. An account is given of the biochemical work of ~fiss Scott Mon-

crieff and g~r Price on the flower-colours. 5. Tt~e in~eraotious of the gone G and the grouping of genes in pairs

are considered. There is some evidence that frol)c~eoZ~,m ~v,@a~ fs a te~ra- ploid.

I ~m indebted to 11{~ H. C. Osterstock for the photograph.

.REFEIRENCES

Ca~,_-r~', M. B. & L~Wl~.¢~CE, W..I, C. (]934). ~V~e Ge~etic~ of Ga.~'de~ PIc~t~. I, on.don: )~aeNillan.

EYscJ~,:a, W. [-t. & Bg~Pm~, D. (1936). "Ii~aeritance of doubleness in the flowers of the nasturtium." J. Here& 27, 51.

Go4zsE~, L. O. (1930). "Chromosome uumbers in ~4a~giosperms. [[ ." &iSlieg~'. get,st. 8, 1'71.

L,~waa~°c]~, W. J. C., P/~tc~, 1R., ~ o ~ s o N : G'. ~![. & 1Ro]~t~sON, ~. (]939). " A survey ofanthocyanh~s. V." BiocAe.m.J. 32, 166I-7.

~io?'~ETT, A. A. (1936). "']'he genetics of T.ropaeoZzon ,mr@~." J. G,,~zst. 33, 151. P~o{sx~sox, .~_. (1.920). "Die Kauptergebnisse yon einigen gene~isehen Versuehen mlt

versehiedenen Formen yon T.ropaeoZ~, Clar]d~ m:d I~npa~iens." Herec~ita.s, L.~d, i , 270.

P~o~i~so~, C4. ~f. & go~mso~, P~, (t931). " A survey of authoeyanins. I f ' Bioche~. J. 25, I687.

(1982). "A survey of anthoc.ganhas. I I . " Bioc]~e~.. jr. 26, 16417. S e o ~ - N o ~ c ~ . , P~, (1936). " A bioohemica,1 survey of some Mendelian factors for

flower colo~a:." jr. Ge~e~. s2, 1t7.

W~Az~,~-, W. G. & F a ~ c ~ , A. P. (1936). '"A genetic study of TropaeoSt'm,. '~ Pro~. Amer. Sov./~o~'~. 6~ci. 34, 5.98.