CELLULAR TISSUE. 13 



16. The cellular tissue is endowed with the power of repro- 

 ducing itself. This is abundantly proved by the existence of 

 vegetables consisting entirely of these cells ; and the extreme 

 rapidity with which they are sometimes generated, is strikingly 

 illustrated by an example given by Prof. Lindley, of a mush- 

 room, the cells of which he estimated to be produced at the rate 

 of four billions per hour. Cells are formed either internally, 

 and the parent cell disappears, or they are formed on the out- 

 side ; and in either case the young cell supplies the conditions of 

 forming new cells. 



17. This tissue, at first soft and mucilaginous, becomes, by 

 age, of a very different consistence, varying remarkably in its 

 composition in different vegetables, and in different parts of 

 the same vegetable. It always commences its existence, as 

 we before remarked, possessed of the same organization, but in 

 its maturity it may become the white, thin, transparent vesicle 

 of the pith of the elder, or the hardened, thickened, unyielding 

 prosenchyma of the wood and the liber. These changes are 

 produced by several circumstances. In the elder all the sub- 

 stance of the cell except the exterior vesicle becomes the food of 

 the plant. The consistence of cellular tissue is most commonly 

 increased by the deposition of a hard matter, sclerogen (skleros, 

 hard, and gennaein, to produce), in concentric layers on the 

 internal wall of the cell. This is often deposited in such quan- 

 tity as to fill the cell, when it becomes very hard and strong, as 

 in the grains of the Quince and Pear, Cocoanut-shell, the seed 

 of the Ivory Palm, and Peach-stone. The deposition of the 

 first layer is generally strictly followed in succeeding layers. If 

 the cell was originally dotted, the dots become pores extending 

 to the center : if in bands or spires, it is the same Fjg 10 



in the hardened cell. Fig. 10 represents a trans- 

 verse section of Fig. 3 filled up. 



18. The parenchymous tissue is in general the 

 depository of all the materials which in vegetables 

 administer to the sustenance of man. It is here we 

 find deposited the material that forms our bread, section of woody 

 from whatever grain it may be manufactured. fiber ' 



It is the cellular tissue, filled with an amylaceous substance, that 

 composes the edible part of the roots that are brought to our 

 tables. The mealiness of potatoes, as it is vulgarly called, is 



16. With what power are cells endowed ? What fact proves it ? How 

 are cells formed ? — 17. How is the consistence of cells altered ? What is 

 the most common cause of the change ? To what extent is it deposited ? 

 What course does it follow ? — 18. Of what is the cellular tissue the depos- 

 itory ? 



