Special Functions and Relations 171 



92. The role of phosphorus. - - Phosphorus is indispens- 

 able primarily because it is a necessary constituent of the 

 nucleo-proteins of every living cell. It is accumulated in 

 relatively large amount in the seed, so in the younger 

 stages of growth, when practically all cells are embryonic, 

 it is relatively most abundant. 



Many observers have commented upon the prompt 

 migration of the sum total of phosphorus compounds 

 from maturing stems and other older vegetative parts 

 to the growing tips or to the developing seeds. It has 

 been shown by Wilfarth and his associates that during 

 the ten days from June 17 to 27, as barley is maturing, 

 there is a striking change in the phosphorus relations, 

 the amount in the straw being reduced from 29.04 kilo- 

 grams to 9.59 ; while in the grain there is an increase in 

 the same time from 3.54 to 29.84 K. per hectare. At the 

 same time they give data which they interpret to mean 

 the movement of some phosphorus back into the soil. 



Loew was the first to suggest important additional 

 functions of phosphorus. As a result of phosphorus 

 hunger the cells of Spirogyra soon cease to grow, but 

 starch is formed for a time. He also found that oily and 

 protein substances were not used, but in fact accumulated 

 in the cell. Owing to the phosphorus content of lecithin, 

 he explained the accumulation of fats by assuming that 

 such substances are changed into lecithin before becoming 

 assimilable by the protoplasm; thus phosphorus would be 

 essential in the assimilation of fats. 



Overton assumes that lecithin and similar bodies are 

 important in the osmotic properties of the plasma mem- 

 brane, this view being largely based upon the penetrability 



