CELLULAR TISSUE. 21 
analysis to be oxygen, hydrogen, and carbon, 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 /ibre. 
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 fruit be 
closely examined, they will 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 the elementary forms 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 fibres will be seen running from 
one portion to the other. Under a microscope these appear to be spiral coils, par- 
tially straitened by being thus drawn out from the membranous tubes in which 
they were lying coiled up. Thus are we able to distinguish the elementary mem- 
brane and fibre, 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 little cells 
which compose it, appears to be, at first globular or egg-shaped, 
but 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 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 brilliant 
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 sda of an inch in diameter, but are found of all sizes, from ao to 3000 
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. 
‘ os é 
