Absorption of Selenium by Plants. 233 
and permanently retained by the plant. With respect to the 
action of the selenate, I could not perceive any difference between 
the plants to which the latter had been applied and those to which 
it had not. I came to the conclusion, therefore, that selenic acid 
applied, at least in small quantities, did not injure plants. 
The next step was to ascertain whether or not the selenic acid 
had been partially absorbed. The plants were accordingly par- 
tially dried, and boiled in strong nitric acid until thoroughly de- 
stroyed. The solution was evaporated to dryness, and the residue 
was treated with dilute hydrochloric acid, which dissolved it 
nearly completely. This solution was concentrated and mixed 
with a saturated solution of sulphurous acid, whereupon the liquid 
assumed at once a deep blood-red colour from the separation of 
seleniunn. 
Before the plants were partially dried they were carefully 
washed, in order to separate any traces of selenate which might 
have adhered to their surface. The application of the selenate 
solution was discontinued for a fortnight before the plants were 
taken up. 
I think this experiment proves that selenic acid is not injuri- 
ous to plants when used in small quantity, and that the acid is 
taken up and retained by plants, or at least by certain varieties of 
plants. The experiment, however, did not prove whether or not 
a partial replacement of sulphur trioxide by selenium trioxide 
had taken place. Having lately become possessed of a large 
quantity of selenium compounds, I hope soon to make experiments 
by growing plants in soil or water free from sulphur, but supplied 
with selenium salts. 
