48 E^ect of Zinc CompouTids 



dissolved zinc compounds find entrance to the tissues by way of the 

 stomates and work injury to the plants. Against this, however, it must 

 be remembered that these same fumes also contain other substances 

 which are admittedly harmful to plant life, and so the deleterious effect 

 may be partly or even chiefly due to these substances rather than to the 

 zinc. Yet it is probable that at least some of the depreciation is due to 

 the zinc. Treboux (1903) tested the effect of zinc sulphate on shoots of 

 Elodea canadensis. If the shoots were placed in ?i/100,000 (= '000016 °/^) 

 zinc sulphate no reduction of assimilation (as observed by counting 

 the number of oxygen bubbles emitted per minute) took place, and 

 replacement in water apparently had no effect either way. When how- 

 ever the shoots were placed in (1) water, (2) "00008 % zinc sulphate, 

 (3) iresh "00008 °/j, zinc sulphate, (4) water again, it was found that 

 while the first solution of zinc sulphate had apparently no effect on 

 assimilation, yet during the second immersion a gradual reduction in 

 assimilation set in, which reduction was continued after the return to 

 pure water, so that the toxic action of the zinc sulphate upon the 

 shoots was clearly demonstrated. 



III. Effect of Zinc on Certain of the Lower Plants. 



Among the fangi, one species stands out in special prominence on 

 account of the great amount of work that has been done on it with 

 regard to its reactions to zinc salts. Aspergillus niger = Sterigmatocystis 

 nigra van Tgh was used as a test plant by Eaulin (1869), who evidently 

 considered that zinc was an essential primary constituent of the food 

 solutions of the fungi, "07 parts zinc sulphate being added to each 1500 

 parts of water. In his experiments he tested (1) ordinary nutritive 

 solution, (2) nutritive solution with various salts added, as zinc sulphate, 

 (3) nutritive solution and salts (as 2) and also powdered porcelain. 



(2) gave a crop of Aspergillus about 3'1 — 3-5 times better than (1), while 



(3) was even better still. Sulphate of iron also proved stimulating in 

 its action, but Raulin stated that zinc cannot replace iron, as both are 

 essential. 



Ono (1900) determined the relation between the weight of the mould 

 crop in grams and the quantity of sugar used up in the presence of 

 varying amounts of zinc sulphate. The amount of sugar used was 

 always greater in the crops with -0037 — -0297 °/„ zinc sulphate by 

 weight than in the control crops, indicating a stimulation caused by 

 zinc. 



