FUNCTIONS OF ROOT-HAIRS 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, 
¥ 
Oars 
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 formation 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, 
