Mineral Solutions and in their Natural Medium . 349 
Weight of 100 plants at beginning of experiment . = 35*8 mg. 
„ „ in Series 1 at end of experiment = 30-8 mg. 
5S „ „ Series II „ „ = 52-8 mg. 
j> >, „ Series III „ „ = 29-4 mg. 
,* „ Series IV „ „ = 50-5 mg. 
A striking feature of the experiment was the fact that although young 
plants were chosen at the beginning, those in mineral salts only never 
increased in size, while those supplied with organic matter rapidly became 
full grown ; and although the energy of these plants was being expended in 
multiplication to a far greater extent than in the control series, yet the * 
individual new plants which were budded off rapidly reached the mature 
condition. The plants in mineral nutrients only seemed to be quite unable 
from the beginning to attain their normal site, and began to multiply in 
their immature state. The figures given indicate quite clearly that Lenina 
major , In common with L emit a minor , cannot maintain its normal health 
and vigour in solutions containing only inorganic nutrients, and although 
Detmer s solution favoured the multiplication of these plants rather better 
than that of Knop, yet there was no appreciable difference in the size and 
health of the plants in the two series. The variation was one of number 
only, and the weights of 100 plants in the two series were practically 
similar at the end of the experiment. Bren ch ley 1 has found that the rate of 
growth of wheat and barley in water culture increases with the concentration 
of the nutrient solution, and the more rapid rate of multiplication in the 
Detmer’s solution may have been due to the greater concentration of 
nutrients supplied in this as compared with Knop’s solution, but in both 
media the plants completely failed to maintain their health. 
Growth of Lemna minor in Pond Water. 
Such mineral solutions as those used in the above experiments, however, 
bear no comparison to the natural habitat of Lemna plants, and in the course 
of the work no comparison had hitherto been made of the growth obtained 
in mineral nutrients and in the water of the pond in which the plants were 
originally growing. Accordingly, in the experiment recorded above, started 
towards the middle of September, an extra set of five dishes was prepared, 
called Series IV and numbered from 15 to 20. These dishes each contained 
150 c.c. of pond water, and the plants were treated precisely as in the other 
series, being counted once weekly, and having the medium renewed twice 
weekly. For each renewal of this series fresh water was obtained from the 
pond, and filtered from suspended matter. 
At the end of the sixth week the plants in this, as in the other series, 
were halved, and the dry weight of one half taken. This was repeated at 
1 Brenchley, W. E. : Annals of Botany, vol. xxx, No. cxvii, 1916, pp. 77-90. 
A a 2 
