16 
A climate that is favorable to a special crop is one whose vicissi- 
tudes of heat and rain and sunshine are not so extreme but that they 
can easily be utilized by the sunbeams in building up the plant. An 
unfavorable climate is one whose average conditions or whose extreme 
vicissitudes are such that the vitality of the plant—namely, its 
power to grow—can not make headway against them. In extreme 
cases, such as frosts, sudden thaws, and great droughts, the climate 
inay even destroy the organic material that had already been formed 
in the plant. 
No plant life, not even the lowest vegetable organism, is perfected 
except through the influence of the radiation from the sun. It may 
need the most intense sunlight of the Tropics, or it may need only 
the diffuse and faint light within dark forests or caves. Heat alone 
may possibly suffice for the roots and certain stages of growth, but a 
greater or less degree of light—i. e., energy delivered in short-wave 
length or rapid periodic oscillations—is necessary for the eventual 
maturity. The radiation from any artificial light, especially the 
most powerful electric light, will accomplish results similar to that 
of sunlight; therefore, it is not necessary to think that life or the 
vital principle is peculiar to or emanates from the sun, but on the 
contrary that living cells utilize the radiations or molecular vibra- 
tions so far as possible to build up the plant. 
We know nothing about the nature of this vital principle, but we 
‘an, by the microscope, demonstrate that the essential ultimate struc- 
ture of the plant or seed is a minute cell, namely, a very thin skin 
or film or membrane inclosing a minute portion of matter consisting 
of mixed liquids and solids. This skin is called the wall of the cell; 
in the early growth of the cell its inclosed liquid is called the proto- 
plasm. By crushing many such young cells we may obtain enough 
of either part to make a chemical examination and find that the cell 
wall is a complex chemical substance called cellulose, composed of 
carbon, hydrogen, and oxygen. By molecules this compound is 
C,,H,,0,,; by weight cellulose has C 44.44, H 6.17, O 49.39 per cent. 
As the cells become older their walls become thicker and are incrusted . 
internally with additional matters, such as gums, resins, ete., until 
the cell wall refuses to perform its original functions. Such old 
cells are not easily digested by man or animals and are not considered 
as food or reckoned among the food crops, but young cells in suc- 
culent stems, leaves, and fruits, or the crushed cells of seeds and 
grains, are nutritious food. Flax, cotton, jute, straw, wood pulp, 
and many other mature dried cells form the important crops of textile 
fibers. 
The protoplasm within the cell is generally an albuminous com- 
