18 CROP GROWING AND CROP FEEDING 



structure of plant cells under a glass of small magnifying power. There are 

 many plants of minute size existing in water that, during all their lives, con- 

 sist of but a single box or cell. Then advancing in complexity we find these 

 cells strung together in threads, then in flat surfaces in a single layer, and 

 finally arranged in numerous forms circling around the stem of the plant 

 to make up the structure. We are so accustomed to look upon a tree as an 

 individual existence that it is hard to realize that it is really a great com- 

 munity of individuals, each doing its work in the way it was set out to do 

 in the beginning and never making any mistake about it. It is hard to realize 

 too, that the framework of the great oak is a lifeless thing, around which 

 life circles in a myriad of forms, while it has entirely abandoned its finished 

 work, and that the central heart wood .takes no part whatever in the vital 

 functions of the tree, but is merely the mechanical support of tfte army of 

 builders which, year after year, add thickness to its stem and wider spread 

 to its branches. This heart may entirely decay and the tree become hollow, 

 and the life still continue to circle around it. 



Hence it is important to know more of the structure and functions of 

 plants in order to fully understand their needs. We have said that all growth 

 is made by the multiplication of these little box-like cells. The tree grows 

 like a building, in which brick after brick is placed in the walls. But in 

 the case of the plant the brick maker and the mason live inside the brick. 

 The walls of the cells contain no life, but are the result of the vital forces 

 contained within them. Every plant cell in its growing state is filled with the 

 substance that carries life with it. This substance has been given the name 

 of protoplasm, or the first thing formed. It is a clear semi-fluid substance, 

 partly granular and partly transparent, and uniform in its appearance. This 

 substance, resembling the white of an egg more than anything else, does 

 all the work of the plant, and it is what in the composition of the plant is 

 called by chemists the albumenoid or protein part. It is itself entirely 

 formless, and yet this formless substance controls the shape of the cell that 

 encloses it, and makes the wonderful variety of forms of cells that we find in 

 the plant by the aid of our microscopes, and little by little builds up the form 

 of the plant, always with an unerring accuracy, so that the final result is such 

 that we recognize the plant as belonging to a certain genus and species, 

 though it may be, and probably is, in some minor points unlike every other 

 plant, even of the same species. 



But as to the essential features, the protoplasm never makes any mistake. 

 The oak may grow beside the pine, and their roots interlock and feed upon the 

 same substances in the soil, while their tops are bathed in the same sunlight. 

 But the. oak never by any chance makes a pine cell, nor the pine an oak cell; 



