452 



Plant Physiology 



The results of stimulation experiments in which seed- 

 plants have been employed are somewhat contradictory. 

 On the whole, a certain degree of stimulation seems pos- 

 sible, especially when some of the conditions of growth are 

 unfavorable. From investigations conducted in Japan 



FIG. 129. Stimulation of growth in Aspergillus by ZnSO 4 (continuous 

 line) and NaFl (broken line). [Data from Richards.] 



there have been reported some benefits from the joint 

 action of iron and manganese, also with salts of iodin, so- 

 dium fluorid, and some other agents, yet some of the effects 

 are probably indirect. 



277. Protection of crops by insecticides and fungi- 

 cides. Practically all cultivated or exploited crops are 

 subject to the attacks of insects and fungi. More than 

 twenty-five important species of insects are known to at- 



