Some Accessory Factors in Plant Growth and Nutrition. 247 



farmyard and other organic manures. The specific action of these accessory 

 substances is not known. They may be concerned in the metabolism of 



o 10 30 40 50 



Time in days 



phosphorus, they may act as catalytic agents, or may be a definite constituent 

 of plant food — a " bau-stein." 



Experiments to test these various hypotheses are in progress. 



In conclusion I wish to acknowledge my indebtedness to Miss F. A. 

 Mockeridge, B.Sc, for her valuable help in the chemical part of this investi- 

 gation. 



