106 PHYSIOLOGICAL ACTIVITIES 



in the nitrogen cycle (page 94), as now believed in, direct 

 from the "decomposition bacteria" to green plants. 



Experiments have been made by different observers in 

 growing seedling plants of various kinds in water culture 

 with one or in some cases several of the amino-acids as 

 sources of nitrogen. Most of these experiments were disap- 

 pointing. Plant proteins are not so different from animal 

 proteins or plant protoplasm (apart from the chlorophyl 

 portions of plants) from animal protoplasm as to lead one to 

 suppose that it could be built up from one 6r two amino- 

 acids any more than animal protoplasm can. The author 

 is strongly convinced that this subject should be thoroughly 

 investigated. It will require careful experimentation and 

 perhaps rather large funds to provide the amounts of amino- 

 acids that would probably be needed, but might result in a 

 decided change in our ideas of soil fertility, and especially 

 in the use of nitrogen fertilizers. 



