CELLULAR TISSUE. 21 



analysis to be oxygen, hydrogen, and cai-bon, with an occasional 

 addition of nitrogen, the same simple elements as, by their 

 varied combinations, constitute the air, water, and most animal 

 substances. The organic basis is simple membrane and Jibre. 

 Of one, or both, of these two forms, all the tissues are con- 

 stricted. 



a. If the fleshy poi-tion of the leaf above mentioned, or the pulp of the frait be 

 closely examined, they vnU be found composed of numerous vesicles of extreme 

 minuteness, adhering together. These vesicles, or bladders, consist of a delicate 

 membrane enclosing a fluid, such as is seen on a large scale in the pulp of an 

 orange. Now this membrane, composing the walls of the cells or vesicles, is one 

 of tlie elementary fonns of vegetable tissue. Again, if the stalk of a strawberry or 

 geranium leaf be cut around but not through, and the two parts be thus pulled 

 asunder for a short space, a number of glistening Jibres will be seen running from 

 one portion to the other. Under a microscope these appear to be spiral coils, par- 

 tially straitened by being tlius drawn out from the membranous tubes in which 

 they were lying coiled up. Tlius are we able to distinguish the elcmentaiy mem- 

 brane and Jibre, of which the various forms of vegetable tissue are composed. 



29. Cellular tissue is so called, from its being composed 

 of separate cells, or vesicles, adhering together. This kind of 

 tissue is the most common, no plant being without it, and many 

 being entirely composed of it. The form of the Httle cells 

 which compose it, appears to be, at first globular or egg-shaped, 

 but afterwards, being flattened at their sides, by their mutual 

 prcssiure, they become cubical, as in the pith, or twelve-sided, 

 the cross-section being six-sided; each cell. assuming a form 

 more or less regular, according to the degree of pressure exerted 

 upon it by those adjacent. It is also called parenchyma. 



a. The cuttings of the pith of elder, or those of any kind of wood, will, under 

 a microscope, exhibit irregular cells and partitions, resembling those of a honey- 

 comb. (Fig. 1, a.) 



b. The vesicles of cellular tissue have no visible communications with each 

 other, but transmit their fluids by invisible pores. 



c. Cellular tissue is transparent and colorless in itself, but exhibits the briUiant 

 hues of the corolla, or the rich green of the leaf, from the coloring matter con- 

 tained within the cells. 



d. The vesicles of this tissue are extremely variable in size. They are usually 

 about -j^ of an inch in diameter, but are found of all sizes, from ^nr to ^nracr 

 of an inch. 



e. Although this tissite is usually soft and spongy, it sometimes acquires con- 

 siderable hardness by the deposition of solid instead of fluid matter in the cells. 



