ELEMENTS OF ORGANIC STRUCTURE. 233 



omists, the distinctions being based either on peculiarities 

 of form or of function. For our purposes it will be neces- 

 sary to define but a few varieties, viz., Cellular Tissue, 

 Woody Tissue, Bast- Tissue, and Vascular Tissue. 



Cellular OF Cell-Tissue 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 structure, being the 

 only form of tissue in the simpler kinds of plants, and 

 that out of which all the others are developed. The 

 term parenchyma is synonymous with cell-tissue. 



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, 

 lignin, and coloring matters, according to their age and 

 position, and are sometimes dotted and perforated, as will 

 be explained hereafter, fig. 53, p. 278. 



Bast-Tissue is made up of long and slender cells, similar 

 to those of wood-tissue, but commonly more delicate and 

 flexible. The name is derived from the occurrence of this 

 tissue in the bast, or inner bark. Linen, hemp, and all 

 textile materials of vegetable origin, cotton excepted, con- 

 sist of bast-fibers. Bast-cells occupy a place in rind, corres- 

 ponding to that held by wood-cells in the interior of the 

 stem, fig. 49, p. 271 . Prosenchyma is a name applied to 

 all tissues composed of elongated cells, like those of wood 

 and bast. Parenchyma and prosenchyma insensibly shade 

 into each other. 



Vascular Tissue is the term applied to those unbranched 

 Tubes and Ducts which are found in all the higher orders 



