68 MISSOURI BOTANICAL GARDEN BULLETIN 
mon example of this phenomenon is the excretion of carbon 
dioxide by the roots, whereby even such resistant rocks as 
marble are corroded and dissolved. In recent years the 
Bureau of Soils of the U. S. Department of Agriculture has 
advanced the idea that the poor growth of a crop on any 
given soil may not be due so much to lack of plant food as 
to the presence of toxic substances arising from the roots of 
the previous crop. In general, though, the amount of any 
excretion from the roots must be very small. 
The purpose of the investigation here reported was to de- 
termine by electrical means the relative amount of exosmosis, 
or excretion, when the plants were subjected to various con- 
ditions. This was done by measuring the electrical conduc- 
tivity, or resistance, of the water before, during, and after the 
roots had been in it for varying periods. Water that is pure 
from a chemical standpoint has a very low conductivity, or 
high resistance, i.e., the electric current passes through lt 
only with difficulty. On adding salts, etc., to the water its 
conductivity increases enormously, hence the measurement 
of the conductivity is likewise a measure of the amount of 
substances which passes from the roots into the water; so 
that in these experiments it is an indication of the excretion 
from the roots. Of course, if the roots are killed, the loss 
of substances from them is very rapid. In these experiments, 
however, it was especially desired to ascertain if unfavorable 
conditions and injurious agents would cause any appreciable 
excretion. 
Some of the plants were accordingly subjected to illumin- 
ating gas, toxic agents, extremes o temperature, and even 
anesthetics and as a result of the tests a definite exosmosis 
was found (variable with the treatment) even when the 
treatment had not been severe or prolonged enough to seri- 
ously affect the plant in its external appearance. With these 
facts before us—and in such detail as they have been worked 
out—it is believed that we can better determine the nature 
and effects of unfavorable field conditions. The work sug- 
gests many new lines of investigation. 
Digestive Ferments of the Marine Algae.—As a result of 
the connection of the Garden, through certain members of 
its staff, with the Marine Biological Laboratory, at Woods 
Hole, Massachusetts, some relations of the marine algae have 
been studied, and especially the digestive processes of these 
organisms have offered some attractive problems. The trans- 
formation of food within the plant is soown to be brought 
about in a way very similar to that in the animal organism, 
—in most cases the same kind of digestive substances or 
enzymes being involved. We know quite well how the com- 
