CELLULAR TISSUE. 21 



analysis to be oxygen, hydrogen, and carbon, witli an occasional . 

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

 varied combinations, constitnte the ah, water, and most anmial 

 snbstances. The organic basis is simple membrane and fibre. 

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

 structed. 



a. If the fleshy portion of the leaf above mentioned, or the pulp of the fniit he 

 closely examined, they A^iil be found composed of numerous vesicles of extreme 

 minuteness, adliering 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 ccUs or vesicles, is one 

 of the elementary forms of vegetable tissue. Again, if the stalls of a strawbeny 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 fibres -will be seen running from 

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

 tially straitened by being thus dl•a^vn out from the membranous tubes in which 

 they were lying coiled up. Thus are we able to distingiush the elemcntaiy mem- 

 brane and fihre.^ of wlaich the various fonns of vegetable tissue are composed. 



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

 of separate cells, or vesicles, adheiiiig together. TMs khid of 

 tissue is the most common, no plant being mthout it, and many 

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

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

 1 ut afterwards, being flattened at their sides, by their mutual 

 pressure, 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 degi-ee 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 Avood, will, under 

 a microscope, exhibit u-regular cells and partitions, rcsembliag 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 imdsible pores. 



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

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

 tained within the cells. 



d. The vesicles of tliis tissue are extremely vaiiable in size. They are usually 

 about ^(j of an inch in diameter, but are found of all sizes, from air to tj ar^^ 

 of an inch. 



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

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



