On the Action of Certain Compounds of Zinc, Arsenic, 
and Boron on the Growth of Plants. 
BY 
WINIFRED E. BRENCHLEY, D.Sc., 
Rothamsted Experimental Station , Lawes Agricultural Trust. 
With seventeen Figures in the Text. 
T HE question of the toxic and stimulant action exercised by various 
inorganic substances on plant life is one round which much controversy 
has circled during recent years. Different investigators have frequently 
obtained discordant results with the same substance, some workers, perhaps, 
claiming for it a stimulative action, while others maintain its universal 
toxicity. The reasons for these discrepancies may be various, but the 
significance of one outstanding fact has not been realized. Experiments 
have been made with plants growing in different substrata, soil, sand, and 
water being the chief media. Results obtained with the one medium have 
often, without adequate proof, been assumed to hold good for another 
medium. Close examination of a great bulk of the literature of the subject 
has shown the fallacy of this assumption, and it is quite evident that a result 
obtained by one experimental method may apparently be contradicted by 
that obtained by another method . 1 In water cultures the experimental 
conditions are very largely under control, but the habitat of the plants is 
unnatural. In sand cultures the investigator is again able to regulate the 
supply of nutrients and poisons, but there comes into play the process of 
adsorption, whereby part of the dissolved substances are withdrawn from 
the solution and removed from the sphere of action by the grains of sand. 
In soil cultures the supply of nutriment to the plant is quite out of control, 
and also the worker has no adequate conception of the interaction occurring 
between the soil constituents and the inorganic substances supplied for test 
purposes. 
As a general rule it is found that the quantity of an inorganic 
substance which exercises a toxic action when presented in water cultures 
is less than that required to exercise a like action in soil cultures. Again, 
1 Vide Brenchley, W. E. : Inorganic Plant Poisons and Stimulants. Cambridge University 
Press, 1914. 
[Annals of Botany, Vol. XXVIII. No. CX. April, 1914.] 
