18 COLLEGE BOTANY 



From a study of the preceding it will be readily seen that 

 the contents of an active living cell are undergoing constant 

 changes and that the cells in various parts of the plant body are 

 different. These changes are extremely complicated and involve 

 the taking in of food materials from the soil and air which are 

 transformed into true food materials, the digestion of foods, 

 the making of new cells, the growth and the modification of cells 

 in various parts of the plant. 



Properties of Protoplasm. Protoplasm has certain very 

 definite and characteristic properties. The most remarkable of 

 these properties is life, which is a characteristic that man has 

 never been able to explain. The other properties will be con- 

 sidered very briefly at this time and be discussed more fully 

 later; they are: (1) movement, which may be seen in the cells 

 of the leaves of Elodea and in the cells from the stamen hairs 

 of Tradescantia and other plants. It is a streaming, circular 

 movement; (2) irritability, in response to stimulation by heat, 

 cold, touch, electricity and other stimulants; (3) assimilation 

 and growth, that is, the taking into itself of compounds which 

 it uses for growth and repair; (4) reproduction, or the ability 

 to make new cells (see page 129). 



Cell Growth and Division. The growth of plants is the sum 

 total of the growth and division of the individual cells of which 

 it is composed. In fact, all the activities of the plant are the sum 

 total of the activities of the living cells of which it is composed. 

 Therefore, the cell is both the anatomical and living physiological 

 unit of the plant. The structure of the living cell and its physi- 

 ological activities are extremely complex. A recent writer has 

 very aptly expressed this idea as follows : " The vital processes 

 exhibited by a cell indicate a complexity of organization and 



