CELLULAR TISSUE. 11 



The cellular tissue is found in all plants : there are 

 even some which are entirely formed of it ; such as the 

 Algae, Fungi, Hypoxylonsj Lichens, and most probably 

 Hepaticae and Mosses, or in other words, all the true 

 Acotyledones. As for other plants, although not en- 

 tirely composed of cellular tissue, it is found in them 

 very abundantly ; it everywhere encircles the vessels ; 

 so that in the vegetable, as well as in the animal king- 

 dom, the vessels are never found destitute of covering : 

 fruits, fleshy leaves, pith, the bark of roots, &c. 

 present a great mass of cellular tissue. Regard being 

 had to proportion, it is more abundant in herbaceous 

 plants than in trees ; in young plants than in those 

 which are aged ; in fleshy parts than in these which are 

 dry and fibrous ; and it seems entirely to compose plants 

 at the period of their first development. The walls 

 which form the cells are of transparent membrane : 

 these easily swell up by maceration in water, and rapidly 

 shrivel and become obliterated by exposure to the air ; 

 so that their examination requires some care. These 

 membranes are generally without colour when they 

 are properly deprived of the sap stored up in the 

 cellules. 



The diameter of the cellules varies much ; in general, 

 the larger it is, the more the part to which it belongs 

 has a loose texture, or the more rapidly it grows. 

 Kieser calculates,, that the largest cellules — those of the 

 Gourd, for instance, or of the Balsam, under a magnify- 

 ing power of 130 times their diameter, are from five to 

 six millimetres ;* and that the diameter of the smallest, 

 as, for example, those of the leaves of the Wallflower, 



* A millimetre is about equal to hh of an inch. It is the thousandth 

 part of a metre, a French measure, which is equal to about thirty-nine 

 inches English. — B. K. 



