PART I. GENERAL ANATOMY 

 CHAPTER I 



CELLS AND TISSUES AND THEIR 

 DEVELOPMENT 



IN the description of the structure and development of the seed 

 plant, it is convenient to consider separately its major vegetative 

 organs, root and shoot Qsfem and leaves'); and, more or less intimately, 

 its structures associated with gametic reproduction, the fiower and 

 fruit. The organs may be resolved into their constituent tissues; 

 and these, in turn, into types and groups of cells, constituting a 

 simple tissue, that are essentially alike in structure and in the 

 functions they perform. 



THE CELL 



The term cell has been variously applied. Early microscopists 

 interpreted it as the box-like unit of structure of which plant and 

 animal tissues are comprised, obviously referring to the cell wall 

 rather than to any included matter. Later, emphasis shifted to the 

 cell contents, or protoplast, rather than the wall. On this basis, 

 a cell may be defined as a protoplast which usually consists of a 

 nucleus, cytoplasm, and various inclusions. (Fig. i.) The term cell 

 is still applied, however, in cases in which the protoplast is lost in 

 the process of differentiation and maturation. Thus tracheids, ves- 

 sel segments, and various types of sclerotic elements which have no 

 protoplast at maturity are frequently referred to as cells in descrip- 

 tive anatomy although it is preferable to use the term element in 

 such cases. The most significant investigations relative to the 

 detailed structure of the cell have been treated by Wilson (45) and 

 Sharp (40). For this reason, the following account is restricted 

 to those aspects of cytology which are most frequently associated 

 with the problems of developmental anatomy. 



