254 HOW CEOPS GROW. 



tides of water or of other liquid matters which thus per- 

 meate the cells. 



THE VEGETABLE TISSUES. 



As already stated, the cells of the higher kinds of 

 plants are united together more or less firmly, and thus 

 constitute what are known as VEGETABLE TISSUES. Of 

 these, a large number have been distinguished by vege- 

 table anatomists, the distinctions being based either ou 

 peculiarities of form or of function. For our purposes 

 it will be necessary to define but a few varieties, viz. : 

 Cellular Tissue, Wood- Tissue, Bast-Tissue and Vas- 

 cular Tissue. 



Cellular Tissue, or Parenchyma, is the simplest of 

 all, being a mere aggregation of globular or polyhedral 

 cells whose walls are in close adhesion, and whose juices 

 commingle more or less in virtue of this connection. 

 Cellular tissue is the groundwork of all vegetable struc- 

 ture, being the only form of tissue in the simpler kinds 

 of plants, and that out of which all the other tissues are 

 developed. 



Prosenchyma is a name applied to all tissues composed 

 of elongated cells, like those of wood and bast. Paren- 

 chyma and prosenchyma insensibly shade into each 

 other. 



Wood-Tissue, in its simplest form, consists of 

 cells that are several or many times as long as they are 

 broad, and that taper at each end to a point. These 

 spindle-shaped cells cohere firmly together by their sides, 

 and "break joints "by overlapping each other, in this 

 way forming the tough fibers of wood. Wood-cells are 

 often more or less thickened in their walls by depositions 

 of cellulose and other matters, according to their age 



