8 Effective Farming 



large. Because of the presence of nitrogen in all the com- 

 pounds, they are often termed nitrogenous, to distinguish them 

 from the others which are termed non-nitrogenous compounds. 

 None of the other classes contains nitrogen. 



Materials determined by the chemist. When making chemi- 

 cal analyses of plants, the chemist determines the water, ash, 

 protein, ether-extract, crude-fiber, and nitrogen-free extract. 

 The meaning of the last three terms requires some explanation. 

 Ether-extract is applied to those compounds that are soluble 

 in ether. They are largely fats, but as yet the chemist is unable 

 to determine the quantity of pure fat in all substances. Crude- 

 fiber includes cellulose and some other bodies that make up 

 the frame-work of vegetable tissue. Nitrogen-free extract 

 is composed of compounds that contain no nitrogen and these 

 are largely starch, sugar, and pentosans. 



7. Structure and functions of plant parts. When a very 

 small portion of plant substance is examined under a microscope 

 of high power, it is seen to be made up of a large number of 

 divisions more or less clearly defined. These are called cells. 

 In a transverse section they present somewhat the appearance 

 of the cells of a honey-comb, which accounts for the name. 

 The higher plants are composed of many cells of different 

 forms; some of the lower plants consist of but a single cell; 

 others, of a single row of cells. A cell is surrounded by a cell- 

 wall and, in the case of live cells, the interior is a semi-liquid, 

 translucent substance called protoplasm. Growth in plants 

 may occur either by the expansion or by the multiplication of 

 cells, which takes place either by the dividing of old cells into 

 two or more smaller ones or by the forming of new cells within 

 old ones, these new cells in either case enlarging later to full size. 



Epidermis and bark of plants. Succulent parts of plants 

 are covered with a thin skin, known as the epidermis, which 

 extends over the entire surface of the leaves, stem, and roots. 

 This skin is made up of fairly thick-walled cells that protect 

 the more delicate interior parts. In the older stems of woody 



