SECT. I. OROANOGRAPHY AND GLOSSOLOGY. 



15 



bladders (fig. 3.). In some 

 cases these vesicles are nearly 

 spherical (a) ; and, in others, 

 they approach the form of short 

 cylinders (6); andin others,again, 

 they are lengthened out, and, 

 tapering at each extremity, pre- 

 sent a fusiform or spindle-shaped appearance (c). 

 The shortest diameters of those cells which are more or 

 less spheroidal, vary from the -j-^n'o to l ^ e ~s$ ^ an ^ nc ^ > 

 but are more frequently found between the -j^ and -j^ Q. 

 The fusiform cells, sometimes termed " closters," which 

 abound in the woody fibre of trees, vary in breadth, at 

 their thickest part, from the -g-Q 1 ^ to the -^-fa of an inch. 

 It is, therefore, entirely owing to the close packing and 

 mutual compression of these vesicles, that they assume 

 a polygonal form in the integral state of the tissue. 

 We may compare the general appearance of this tissue 

 to a mass of froth, obtained by blowing bubbles in 

 soap suds or gum water. The bubbles, by mutual 

 pressure, assume a polygonal structure towards the 

 centre of the mass, but have spherical surfaces towards 

 the outside. In the cells which are thus formed, 

 however, each cavity is separated from its neighbour by 

 only a single partition; whilst, in the vegetable tissue, 

 each partition is of course double. As the cellular 

 tissue alone, without tubes, exists in a large class of 

 plants, it is evident that the most general functions of 

 vegetation must be carried on by it : but, as such an 

 inquiry belongs to the physiological department, we 

 need not say any thing concerning it at present. 



(17.) Polygonal Structure. If 

 we place a number of equal circles 

 in contact, on a plane surface, 

 each circle may be touched by 

 six others ; and if we suppose 

 them to be so pressed together, 

 that the curvature of each circle 

 at the points of contact may pass 



