FORMATION OF VEGETABLE STRUCTURE. 



other moist surfaces. In this last case, a simple detached cell exercises the 

 functions of an entire independent organism, imbibing and elaborating 

 extraneous matter, extending itself by the process of growth, and continuing 

 its species by generating other cells of the same kind. Even in the aggre- 

 gated state in which the cells exist in vegetables of a higher order, each cell 

 still, to a certain extent, exercises its functions as a distinct individual ; but 

 it is now subject to conditions arising from its connection with the other 

 parts of the plant to which it belongs, and is made to act in harmony with 

 the other cells with which it is associated, in ministering to the necessities 

 of the greater organism of which they are joint members. These elementary 

 parts are therefore not simply congregated into a mass, but combined to 

 produce a regularly organised structure ; just as men in an army are not 

 gathered promiscuously, as in a mere crowd, but are regularly combined for 

 a joint object, and made to work in concert for the attainment of it ; living 

 and acting as individuals, but subject to mutual and general control. 



Now the varied forms of tissue found in the higher orders of plants do 

 not exist in them from the beginning ; they are derived from cells. The 

 embryo plant, like the embryo animal, is in its early stages entirely formed 

 of cells, and these of a very simple and uniform character ; and it is by a 

 transformation of some of these cells in the further progress of development 

 that the other tissues, as well as the several varieties of cellular tissue itself, 

 are produced. The principal modes, as far as yet known, in which vegetable 

 cells are changed, are the following. 



1. The cells may increase in size ; simply, or along with some of the 

 other changes to be immediately described. 



2. They alter in shape. Cells have originally a spheroidal or rounded 

 figure ; and when in the progress of growth they increase equally, or nearly 

 so, in every direction, and meet with no obstacle, they retain their rounded 

 form. When they meet with other cells extending themselves in lik& 



Fig. II. 



Fig. III. 



Fig. II. TEXTURES SEEN IN A LONGITUDINAL SECTION OF THE LEAF-STALK OF A 

 FLOWERING PLANT. 



Fig. III. STELLATE VEGETABLE CELLS. 



manner, they acquire a polyhedral figure (fig. n. , 1 2 ), by mutual pressure of 

 their sides. When the growth takes place more in one direction than in 

 another, they become flattened, or they elongate and acquire a prismatic, 

 fusiform, or tubular shape (fig. n. , 3 4 3 ). Sometimes, as in the common 

 rush, they assume a starlike figure, by mutual adhesion of their walls at 



