CHAPTER I 



THE CELL 



It has been recognized since the seventeenth century that living 

 beings, particularly plants, are composed of cells. The English 

 investigators Hooke and Grew in the latter half of that century 

 noted the fact that the body of vegetable organisms was often con- 

 stituted of minute chambers, and to these Hooke first gave the 

 name of cells. Grew was apparently the originator of the term 

 "tissue," and he compared the organization of plants with the 

 woven texture of lace. A clear conception of the cellular structure 

 of living beings was not, however, reached until nearly two centu- 

 ries later. Plants differ from animals in the fact that their gross 

 internal organization is of relatively slight scientific importance 

 compared with the more obvious bony and muscular structures of 

 the animal body. The anatomy of plants is thus essentially a 

 matter for microscopic investigation. Some knowledge of the 

 general features of the structure of the cell in plants is accordingly 

 necessary as a preliminary to the more detailed pursuit of anatomy. 



The cell in vascular plants has certain features which bring it 

 into sharp contrast with the corresponding unit of structure in the 

 higher animals. The essential substance of all living cells is proto- 

 plasm, simply distinguished from inanimate matter by the posses- 

 sion of a capacity for change and reproduction, which does not 

 characterize matter devoid of life. In the higher plants the proto- 

 plasm does not show the large degree of solidity which is a feature 

 of the animal cell, but is ordinarily reduced to a thin vesicle sur- 

 rounding a larger or smaller central cavity known as the vacuole. 

 The bladder-like protoplasmic vesicle is rendered possible in plants 

 by a containing, supporting, and likewise more resistant envelope 

 called the cell wall. This wall is not nitrogenous in its chemical 

 composition, as is true of the living protoplasmic body, but is, primi- 

 tively at least, a ternary compound, containing carbon, oxygen, 

 and hydrogen, the first-named element being the most abundant. 



