364 Bottom ley , — The Effect of Organic Matter on the 
When organic substances were added to the culture solutions the 
plants, whether young or full-grown, grew quite normally and reproduced 
themselves rapidly, the offspring rapidly reaching the normal size. 
The effective organic substances were found to be present in an auto- 
claved growth of Azotobacter chroococcum , crude nucleic acid derivatives 
from raw peat, and a water extract of bacterized peat. 
Similar trials carried out with Salvinia natans showed that these plants 
also are unable to maintain themselves in health without the presence of 
organic growth-promoting substances. The plants originally placed in 
mineral nutrients only remained healthy, but all new leaves formed were 
successively smaller and more yellowish in appearance. The addition of 
organic matter to the solution resulted in a more rapid rate of growth, the 
new leaves formed rapidly reaching the full normal size, and remaining 
perfectly healthy in appearance. 
Azolla filiculoides also responded to the presence of organic substances 
in the culture solution, although not to quite the same extent as in the case 
of the plants mentioned above. The control plants, in minerals only ? 
remained healthy for a longer period than did the controls of these other 
plants, probably on account of the symbiotic habit of Azolla , which would 
of necessity result in the supply of a certain quantity of organic matter to 
the plants. 
Plants of Limnobium stoloniferum were also experimented with, and it 
was found that the addition of organic substance materially improved the 
health and size, as indicated by weight, of the plants. In these, as in the 
preceding experiments, a marked effect of the organic addition was its 
influence on the colour of the plants, those in minerals only becoming 
yellowish after a time, while those supplied with organic substance retained 
their green colour. 
In no case did the organic substance supplied exceed 184 parts per 
million, while the concentration of salts in the culture solution totalled 5,500 
parts per million. 
Throughout the experiment it was found that the more rapid the rate 
of multiplication of the plants, the quicker was the response to the addition 
of organic substance to the solution. 
The plants, in nature, obtain their supplies from the water of the. 
ponds and streams in which they grow, and the quantity of these organic 
substances present in their tissues at the beginning of the experiment will 
necessarily diminish more rapidly as their rate of multiplication is increased. 
The more rapidly-growing plants therefore respond more quickly to the 
addition of organic substances in their culture solutions. 
