354 Bottom ley. — The Effect of Organic Matter on the 
The question arose as to whether this necessity for organic matter is 
a peculiarity of water plants as distinct from land plants, and whether, 
among water plants, Lemna stands alone in such requirement. A preliminary 
experiment has already been reported with Lemna major l which indicated 
that the behaviour of this plant corresponds with that of Lemna minor 
in that it fails to grow normally in a mineral solution, while the addition of 
water-soluble organic matter from bacterized peat enables it to maintain its 
health and increase its rate of multiplication. This experiment, however, 
was essentially of a preliminary nature, and was carried out towards the 
end of the growing season when no rapid multiplication could be expected. 
Experiments with Lemma major. 
A more extensive trial with Lemna major was made about the middle 
of May, to determine whether this plant would still fail to grow well in 
mineral nutrients even during the good growing season, and also to discover 
whether organic substances other than bacterized peat could supply the 
deficiency in this case as in the case of Lemna minor. 
Four series of five dishes each were arranged, each containing 150 c.c. 
of Detmer’s solution. The dishes of Series I, numbered from 1 to 5, served 
as controls, while the following additions were made to the other dishes : 
Series II, numbered from 6 to 10, the crude nucleic acid derivatives from one 
gramme of raw peat in every 500 c.c. of solution ; Series III, numbered from 
11 to 15, one gramme of autoclaved Azotobacter growth in every 1,000 c.c.; 
and Series IV, numbered from 16 to 20, the water extract of one gramme of 
bacterized peat in every 500 c.c. These various substances were obtained 
in precisely the same way as described in the previous publications. 
Ten plants of Lemna major were counted out into each dish, and care 
was taken to select very young plants, instead of full-grown ones, in order 
that their size might be more uniform. Three hundred similar plants were 
taken at the same time and well washed for an estimation of their dry 
weight, which was found to be 24-2 mg. for 100 plants. 
The dishes were surrounded up to the level of the liquids with paper 
which was black on the side towards the dish and white towards the outside, 
in order to exclude light from the bottom and sides. The whole set was 
covered with a large sheet of glass supported a little above the top of the 
dishes, in order to prevent the access of dust as much as possible. The 
solutions were changed twice weekly, and the plants counted once weekly, 
care being taken to exclude green algae as much as possible. The figures 
obtained in the first three weeks of the experiment are shown in the table 
below : 
1 Bottomley, W. B. : Annals of Botany, vol. xxxiv, No. cxxxv (1920). 
