26 PLANT LIFE ON THE FARM. 
into soluble bicarbonates, and exercises a similar power 
of solution in the case of phosphates. 
Leaves and Leaf Action.—The two great factors in 
the feeding of the plant are the roots and the leaves. 
The soil supplies to the roots, as we have seen, water in 
large quantities, gases, earthly and saline substances ; 
but the air is an equally important source of nourish- 
ment, or even more so, since there are rootless plants, 
and plants which receive no part of their food directly 
from the soil, while no plant can exist without air, and 
no plant that is of direct importance to the cultivator 
can live without light. We insert the word “‘ direct” 
because there is a whole group of plants which can thrive 
in the absence of light, but these form no part of the 
ordinary crops of a farm. Indirectly, however, as has 
been pointed out, in considering the agency of bacteria 
as ferments in the soil, these organisms to whose career 
light is not essential may be of the greatest consequence 
to cultivators ; and it is probable that the future will 
show us much more fully how great is our indebtedness 
to them. For our present purpose, we have to deal with 
plants producing leaves, to point out some of the work 
which the leaves do, and to give some indication of how 
they do it. 
Unlike the root, which originates from within the sub- 
stance of the plant and breaks its way out to the surface, 
the leaf, as has been stated, is a direct production from 
the surface of the stem or branch. It is one of the char- 
acteristics of a root not to produce leaves ; it is one of the 
attributes of the stem and its subdivisions to clothe 
themselves with these appendages. 
In form, texture, size, the leaf presents infinite variety. 
Sometimes it is a mere dry scale, sometimes a thick, 
fleshy excrescence; now it offers a broad, banner-like 
surface, now it is reduced to the form and dimensions of 
