Effect of Zinc Compounds 47 



The marked individuality in the response of the various plants to the 

 poison is very striking. Allium showed signs of increased growth 

 throughout; Pisum was apparently improved in the early stages of 

 growth, but when the dry weights were taken at the end of the experi- 

 ment no increase manifested itself in the weights of the plants treated 

 with zinc ; with Hordeum the same quantity of zinc exercised a con- 

 sistently injurious action. These results with peas and barley corroborate 

 those obtained in the Eothamsted experiments with water cultures in 

 that zinc sulphate proved to be less toxic to peas than to barley. 



Kanda found that both peas and beans when grown in soil as pot 

 cultures were improved by larger quantities of zinc sulphate than when 

 they were treated as water cultures — a result in full accordance with 

 current knowledge. 



Wheat is evidently peculiarly sensitive to the effects of zinc com- 

 pounds under differing conditions. Javillier (1908 c) pointed out that 

 while wheat is very susceptible to the toxic action of zinc, yet it can 

 benefit by the presence of sufficiently small quantities of the compounds 

 of the metal. Rice is another cereal that is said to respond to the action 

 of ziac sulphate, as Roxas, working in pot cultures with soil both with 

 and without the addition of nutritive salts, obtained an acceleration of 

 growth on the addition of m/1000 zinc sulphate, a quantity so remark- 

 ably great that it might be expected to act as a toxic rather than as 

 a stimulant. 



With phanerogams the zinc question is not only concerned with the 

 effect of the metal upon germination, but also with its effect upon the 

 later growth of the green plants, and on the physiological functions 

 involving the construction of substances at the expense of mineral 

 elements and the carbon dioxide of the air. Javillier holds that the 

 indications are that zinc would prove to be profitable if applied to crops 

 as a " complementary " manure. 



4. Direct action of zinc salts on leaves. 



Dandeno (1900) applied zinc sulphate in drops to the leaves of 

 Ampelopsis, and found that the solution was not all absorbed by the 

 leaf, but that a slight dark ring of a yellow colour was produced, and he 

 was induced to think that some local stimulation was produced if the 

 salt was presented in sufficient dilution. 



Klopsch (1908) discussed the effect on plant growth of zinc derived 

 irom industries producing zinc fumes. Zinc oxide fi-om the fumes is de- 

 posited on the leaves, and Klopsch stated that the rain and dew containing 



