LIFE OF A PLANT 
minerals soluble, and by a strange intelligence, 
select the kind and amount of material they take 
in. In certain groups of plants, notably the 
Legumes, colonies of Bacteria take the place of 
root hairs, and by a reciprocal action, provide 
the plant with the nitrogenous elements which 
it craves. 
The principal food of most vital importance 
taken in by the roots is nitrogen. Nitrogen is 
one of the basic elements of protoplasm, the 
life fluid of the living cell. Where there is 
life, there is nitrogen. Sulphur, phosphorous, 
silica, iron and other elements are also needed 
in small quantities. 
The root hairs are constructed so as to allow 
fluids to pass in but not out. The continual ab- 
sorption of water results in a mechanical pres- 
sure which automatically forces the sap up 
through the stem to all parts of the plant. The 
process is aided by the evaporation of water 
from the leaves, through the partial vacuum 
created by them at the top of the system. 
Pushed from below and pulled from above, 
the sap of a tree, for instance, moves with a pro- 
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