14 COLLEGE BOTANY 



involving growth, wast and repair (see Chapter XVIII), and 

 (c) the power of reproduction (see Chapter VII). The chemical 

 composition of living protoplasm cannot be accurately deter- 

 mined, since the methods employed by the chemist must neces- 

 sarily result in the death of the protoplasm. Therefore, the 

 analysis must be made of the dead protoplasm, which probably 

 differs in some degree from the living protoplasm. However, it 

 is evident that protoplasm contains carbon, hydrogen, oxygen, 

 nitrogen, sulfur and in some cases other elements. We are 

 unable to distinguish differences between plant and animal pro- 

 toplasm, or between the protoplasm of low and high forms of life. 



The protoplasm is composed of two parts, the cytoplasm and 

 the nucleus. The cytoplasm appears granular or web-like, depen- 

 dent upon the power of the microscope in use, and may be com- 

 pared to an extremely delicate sponge. The spaces between the 

 delicate web or net-like structures are known as vacuoles and are 

 usually filled with cell-sap, which consists of water containing 

 sugar, salts and other soluble materials. Every free surface of 

 this cytoplasm (such as the outer surface and the surfaces of 

 the vacuoles) is organized into what is known as the plasma, mem- 

 brane, which is evidently very important but is not well under- 

 stood. It is about .0003 inch thick and lies so close to the cell 

 wall that it is very difficult to detect. However, it can be demon- 

 strated by treating the living cell with 5 per cent, salt solution, 

 which causes the protoplasm to shrink. 



The nucleus of the cell was discovered by Robert Brown 

 (Fig. 5), an Englishman, in 1831. It is usually spherical, is 

 composed of dense protoplasm, which is sometimes called " nucle- 

 oplasm," and is surrounded by a delicate membrane known as 

 the nuclear membrane. It usually contains one, sometimes more. 



