THE DEVELOPMENT OF AGRICULTURAL CHEMISTRY 13 



on the unique ability of living cells to produce essential controlling 

 agents, called enzymes. 



The Cell 



The science of biology teaches us that the cell is the biological unit 

 of life. Chemistry and physiology have shown that these tiny units may 

 be likened to factories, each receiving its raw materials from which it 

 not only fabricates its own building materials but, in addition, often 

 furnishes essential materials for other cells elsewhere in the living 

 organism. 



Animal cells are covered by a protoplasmic membrane, whereas 

 plant cells usually possess two membranes, one consisting of modified 

 protoplasm similar to that of the cell itself, and a second membrane 

 or heavy wall consisting of cellulose. 



The living plant cell is, in reality, a protoplast, that is, a droplet of 

 organized protoplasm enclosed in a cellulose compartment. When 

 such a cell is plasmolyzed by immersion in a salt solution of higher 

 concentration than that of the cell itself, the cell loses its characteristic 

 turgidity and the protoplasmic membrane draws away from the cellu- 

 lose covering. 



The typical cell contains a spherical or semispherical body called a 

 nucleus. If the nucleus is removed, the cell loses its power of reproduc- 

 tion. Certain cells have several nuclei, and a few are non-nucleated, 

 for example, the red blood cells in man. 



Although cells of plants and animals differ in many respects, we find 

 that both types of cells contain, as their principal structural substance, 

 a liquid or semiliquid form of matter known as protoplasm. Careful 

 chemical studies of plant and animal protoplasm indicate that both 

 types are essentially similar in their chemical and physical charac- 

 teristics. 



Protoplasm 



Protoplasm is a translucent, grayish, shiny substance similar to a 

 thin jelly in consistency. To use another example, protoplasm has 

 properties similar to those of fresh egg white. Under the microscope it 

 appears to consist of a thick matrix containing globules and granides. 

 Chemically, protoplasm seems to be a colloidal system consisting of 

 water (about 75 per cent) and solid matter (about 25 per cent). 

 Protein is a major solid constituent. Other chemical constituents of 

 protoplasm include sugars, lipides, amino acids, and inorganic salts. 



At first glance it would appear that protoplasm is a rather simple 



