FUNCTIONS or EOOT-HAIES 



169 



impossible for the plant to continue its life functions. 

 The indispensable plant-foods gathered from the soil 

 by the root-hairs, in addition to water, are : potas- 

 sium, calcium, magnesium, iron, nitrogen, and phos- 

 phorus, — all in their proper combinations. How the 

 plant uses these substances is yet poorly understood^ 



Fig. 39. Penetration of a root-hair through soil. 



but we are fairly certain that each one has some 

 particular function in the life of the plant. For 

 instance, nitrogen and phosphorus are probably 

 necessary in the formatitjn of the protein or the 

 flesh-forming portions of the plant, while potash 

 is especially valuable in the formation of starch. 



There is a constant movement of the indispensable 

 plant nutrients after they have entered the root-hairs. 



