STRUCTURE. 57 
cast into an infinite variety of forms. We have 
seen how the roots absorb nutriment from the 
soil, and what organs act as the means of commu- 
nication. It remains to be shown that the means 
by which the leaves absorb their gaseous food 
from the atmosphere, are those provided by the 
existence of minute orifices in the leafy surfaces— 
chiefly on the under surface of the leaves. These 
orifices—called stomata—are oval in shape, and 
are very abundant; so much so indeed, that ina 
single leaf of some Trees—the Apple will furnish a 
familiar example—there have been counted more 
than a hundred thousand! Through their sto- 
mata, or breathing pores, plants not only absorb air 
but give out their surplus moisture ; and thus by 
the superabundance of the liquid which they derive 
by their roots from the earth, they are enabled to 
promote, around the tender forms of their leaves, 
the congenial moisture which is so conducive to 
healthy life and to vigorous growth. 
