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 

 may 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 gi'owth, 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 

 can, 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 groAvth of the cell its inclosed liquid is called the proto- 

 v' ism. By crushing many such young cells we may obtain enough 

 \ iither 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 

 CisHgyO.s; 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, etc., 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- 



