VOL. 74, No. 1926

number of healthy plants were obtained and washedthoroughly with sterile water. They were then im-mersed for an instant, one at a time, in 95 per cent.alcohol followed by one minute in HgCl2 solution1: 1,000 and then rinsed in several changes of sterileacid phosphate solution. From this the plants weretransferred to Knop's solution plus 0.5 per cent. ofdextrose. In this manner six or eight pure cultureswere obtained. It is suggested that this method mayovercome the difficulties mentioned by Saeger5 in con-nection with the direct disinfection of the fronds.

Experiments to determine the relation of manganeseto the growth of Lemna were made on solutions freedfrom manganese in two ways. In the first case thechemicals used in the preparation of Knop's solutionwere recrystallized three times from conductivitywater. In the other case manganese was removedby absorption on calcium phosphate at pH 8.0 as inthe work with Chlorella. This latter solution whichcontained dextrose was acidified and its calcium con-

tent increased by adding to it a sterile solution ofrecrystallized calcium nitrate and potassium hydrogenphosphate. This procedure was resorted to becauseof the difficulty encountered in removing manganesefrom glucose by recrystallization. Known amounts ofiron (1: 500,000) were added to each culture from a

solution prepared from recrystallized ferric alum andrecrystallized sodium citrate. For plus manganese

cultures manganese sulphate was added to give a con-

centration of Mn of 1: 5,000,000.In the first experiments without dextrose the con-

trols showed no development of fronds and no rootformation while with manganese 1: 500,000 there was

good development of green fronds and healthy rootgrowth. In fact the fronds planted in the controlflasks finally became chlorotic and died. In table Ithe results of such an experiment are given.

TABLE ITHE NECESSITY OF MANGANESE FOR THE GROWTH OF

Lemna minor (WITHOUT DEXTROSE)

Green fronds (54 days)

+ Mn .127 (5 cultures)

-Mn .9 (5 cultures)

In the later experiments the presence of dextrose(0.5 per cent.) made it possible to obtain results in a

shorter time. The summarized data from one of theseexperiments is given in Table II.The necessity of manganese for Lemna is clearly

shown in the above data both with and without ironbeing added. In the latter experiment after the

5Albert Saeger, "A Method of Obtaining Pure Cul-tures of Spirodella polyrhiza," Bull. Torrey Bot. Club57: 117-122, 1930.

TABLE IITHE NECESSITY OF MANGANESE FOR THE GROWTH OF

Lemna minor (WITH DEXTROSE)

Per cent. increasePer cent. increase in 15 days after

Treatment in no. of fronds transferring onein 21 days plant to another

set of culturesolutions

-Pe-Mn 222 (5)* 0 (5)-Fe+Mn 769 (5) 810 (5)+Fe-Mn 90 (5)0 (5)+Fe+Mn 843 (5) 1160 (5)

* The figures in parenthesis refer to the number ofcultures in each case.

seeond transfer the plants without manganese showedno development at all and finally died. The plantswith both iron and manganese were very healthyin appearance with large deep green fronds. Thosewith manganese and without iron were smaller andehlorotic. Since the dry weights of the plants agreeclosely with the counts of the number of fronds thesedata are not given here. An interesting occurrence isthe development of definite symptoms of manganesedeficiency consisting of depressed root formation andof light brownish to white necrotic areas on thefronds in the case of those cultures without manga-nese.

I believe that these experiments which have beenrepeated a number of times with the same result showconclusively that manganese is an essential elementfor Lemna and suggest that it is undoubtedly neces-sary for the growth of all green plants.

E. F. HOPKINSCORNELL UNIVERSITY

LABORATORY OF PLANT PHYSIOLOGY,

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