Growth of various Water Plants in Culture Solution . 359 
All the above figures indicate that, as in Lenina , not only is the rate of 
multiplication less in Detmer’s solution without the presence of the growth- 
promoting organic substances, but there is also a diminution in size of the 
individual leaves as indicated by their weight. These facts were also very 
evident from the general appearance of the plants. The original plants 
placed in mineral nutrients only remained fairly healthy throughout the 
experiment, but the new leaves arising from them became successively 
smaller and more yellow in colour, indicating some interference with the 
metabolic activities of the plants. Those supplied with the organic sub- 
stances remained perfectly healthy throughout the experiment, the new 
leaves arising becoming fully as large- as, and in some cases larger than, 
the original ones. PI. XVII, Fig. 3, shows a photograph of the whole set of 
dishes, taken in the last week of the experiment, and PI. XVII, Fig. 4, shows 
one representative dish from each series on a larger scale taken at the same 
time. Both the difference in rate of multiplication of the leaves and the 
variation in their size are clearly shown in these two photographs. 
Experiment with Azolla filiculoides. 
A set of ten dishes, divided into two series of five dishes each, was 
prepared in precisely the same way as for the Salvinia experiment. Into 
each of these dishes were counted out ten small sprigs of Azolla filiculoides , 
the sprigs being as nearly alike as possible. Since it was impossible to 
estimate the number of leaves on this plant, the number of visible growing- 
points was counted, and the total number of growing-points introduced into 
each dish on the ten small portions of Azolla was eighty. Four similar 
sets were counted out at the same time, and their dry weight was estimated. 
The figures obtained were 16-4, 17-0, i6-8,and 16-6 mg. respectively, giving 
an average of 16-7 mg. as the dry weight of the original contents of each 
dish. * 
The culture solutions were changed twice weekly and the number of 
visible shoots counted once weekly. At the end of the fourth week the 
plants in Series II had filled their dishes, so the contents of all the dishes 
were halved, one half being retained and the dry weight of the other half 
estimated. This was repeated at the end of the fifth, sixth, eighth, and 
eleventh weeks. 
The weekly figures for each dish are shown in the table below, the 
number of shoots being given in the upper portion of the table and the 
weights in the lower part. The figures given represent those for the com- 
plete set each week, and not for the fractions of the complete sets (one- 
thirty-second part) which were actually in the dishes after the fourth week. 
The contents of dishes No. 3, 4, 8, and 10 were pressed and mounted 
as a permanent record, and photographs of these pressed plants are shown 
in PI. XVII, Figs. 5 and 6. 
