1 6 General Botany 



In young plant cells the protoplasm occupies all the space 

 within the walls. As cells grow older and enlarge, small cavities 

 containing water appear in the protoplasm. As the cell takes up 

 more water, these cavities, or vacuoles, expand and unite, until 

 finally there is a single large vacuole within the protoplasm, con- 

 taining the cell-sap. There are, then, three primary divisions 

 of the plant cell : the protoplasm, the vacuole, and the cell wall 

 (Fig. 6). ^ 



Protoplasm. The living matter of the cell when active has 

 about the same consistency as the white of egg. Active proto- 

 plasm contains a large amount of water, while in dry seeds the 

 protoplasm contains less water and may be quite rigid. Like 

 gelatine, protoplasm is more or less liquid when it contains a 

 high percentage of water ; when it contains smaller amounts of 

 water it becomes more nearly soKd. The abihty to absorb 

 and hold large amounts of water is one of its most important 

 qualities. 



In composition protoplasm is very complex and may vary 

 considerably, not only in different plants and in different parts 

 of a plant, but also in the same cell, as a result of a change of 

 environment or of increasing age. Analyses show that aside 

 from water about one half of the protoplasm consists of protein. 

 The remainder is made up of sugars and other carbohydrates, 

 fats, and smaller amounts of salts and other substances. In 

 some manner that is not fully understood at present, the com- 

 ponents of protoplasm maintain a continuous group of activities 

 which result in the phenomena known as life. Its most remark- 

 able property is its abihty to take up food and to construct from 

 it more protoplasm like itself. 



Protoplasm can also use food substances as a source of energy, 

 and it carries on physical and chemical processes with the energy 

 thus obtained. These processes are regulated in one way or 

 another by the protoplasm itself. We may, therefore, look upon 

 protoplasm as a body of matter that can absorb food materials, 



