Growth of various Water Plants in Culture Solution. 361 
A comparison between the number of shoots in the two series is 
readily obtained by putting the average number in Series I at 100 for each 
week, when the corresponding numbers for Series II are obtained for the 
twelve weeks — 99, 107, x 26, 128, 146, 163, x6i, 147, 148, 153, [85, 172. 
The fluctuation in these ratios from week to week is no doubt due to the 
unequal growth which had taken place during the varying weather 
conditions. 
A corresponding comparison between the weights of the plants, putting 
the weight in both series at 100 for the beginning of the experiment, shows 
for Series II for the 4th, 5th, 6th, 8th, and nth weeks respectively, the 
figures 126, 144, 152, 129, and 142. 
It Is evident from these figures that the plants of A solid filiculoides 
respond to the presence of organic growth-promoting substances, although 
the response is not so niarked as in the case of Salvinia and Lemna. 
A solid plants, however, have long been known to be associated with an alga, 
Anabaena , which inhabits special cavities in the plants ; and these cavities 
have also been shown by the writer 1 to contain nitrogen-fixing organisms. 
The symbiotic nature of these plants is a factor which must be taken into 
consideration in any discussion of their nutrition, since it is quite probable 
that such an association may furnish the platlt with a proportion of the 
necessary organic substances for its metabolism. Under these circumstances 
a smaller response to the addition of such substances than is the case in 
a normal plant Would be expected ; and it was the fact that these plants, 
in the mineral solution only, retained their healthy appearance to a much 
greater extent than in the case of the plants with which the previous trials 
were carried out. 
The increase in weight of these A solid plants grown in the solution 
containing organic matter was not quite commensurate with the increase in 
number of the shoots, but this is readily explained by the fact that the 
main shoots of the control series elongated rather more than did those in 
Series II, before giving rise to secondary shoots. Hence the average 
weight of the shoots in Series I is greater than that in Series II, although 
in the latter series the total weight and number of the shoots are markedly 
superior to those in Series I, indicating a better nutrition of the plants. 
Experiment with L imnobium stol onifer um. 
On September 22 a number of small plants of Limnobium stoloni- 
ferum were obtained, sufficient to start two small series of four dishes each. 
Four of these dishes (Series I) contained 300 c.c. of Detmer’s solution, and 
the other four (Series II) 300 c.c. of this solution containing also the extract 
of one gramme of bacterized peat in every 1,000 c.c. Into each dish six 
plants of Limnobium were put, care being taken to select all eight sets as 
1 Bottomley, W. B. : Report Brit. Ass., 1910, pp. 786-7. 
