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 or 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 toa 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 wcod-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 
