10 STRUCTURE AND PROPERTIES 



shown that the solid structure of plants consists 

 of, Cellular Tissue, Vessels, Fibres, and Skin. 

 2. Cellular Tissue (contextus cellulosus), is 

 a membranous tissue, very similar in arrange- 

 ment and form, to a honeycomb, being com- 

 posed of detached cells, as its name denotes, 

 which are closed, and adhere more or less nearly 

 together it is found universally in all plants, 

 and many of the lower tribes, such as lichens, 

 mosses, &c. are entirely formed of it. It sur- 

 rounds the vascular parts so that in the vege- 

 table as in the animal conformation, no vessel is 

 ever exposed and bare. The diameter of the 

 cells, or vesicles, which is perhaps their more 

 correct appellation, varies considerably, from 

 the thirtieth to the three thousandth of an inch ; 

 their shape also is much diversified, but the 

 normal form appears to be round, and it is pro- 

 bable, indeed almost certain, that the variety 

 depends on the pressure of one part of the plant 

 on another during its growth. ' The vesicles 

 seem to originate from a point, called by mo- 

 dern writers a cytoblasl,* which sometimes con- 

 tinues visible after they have reached maturity. 

 The property of uniting firmly together, pos- 



* Probably from KVTOQ a cavity or hollow point, /3Xa<ro 

 a branch or sprout. 



