102 
PHYSIOLOGICAL VIEWS. 
almost destitute of any kind of sensation, and yet they are ranked among animal 
substances. 
116. The vegetable S'lbstance consists of parts, called by the 
general name tissue^ divided into Cellulak and Yasculae. 
The chemical basis of this tissue is carbon, oxygen, and hydro 
gen, and, in a few cases, a small 
proportion of nitrogen ; the organic 
basis is membrane and Jlher. The 
membrane forms ovoid cells (Fig. 
122, «), while the fiber is elongated 
into tubes {hod). It seems that, 
primarily, all vegetable tissue is 
cellular or membraneous, and that by the fixation of carbon in 
the membraneous substance, is formed the harder, vascular tis 
sue, which gradually becomes fibrous ; (thus, c d, Fig. 122, 
show the cells, seen at a becoming vascular). 
117. Cellular tissue, Paeenchyma, consists of cellules 
(minute cells or vescicles) adhering together ; at first they are 
of a roundish form, but by the action of their mutual pressure 
they become elongated and flattened at the sides, and some- 
times assume an hexagonal appearance, like the cells of honey- 
comb ; in some cases this tissue resembles the froth of fer- 
menting liquor. 
Fig. 123, a, represents the hex- 
agonal cellular tissue of the pith of 
Sambucus (the elder plant). The 
size of cells varies from one-twen- 
tieth to one-thousandth of an inch 
in diameter. The cellules are lar- 
gest in the most rapid growing 
parts of the plant, as in the Gourd ; 
they are destitute of visible pores, 
but fluids are transmitted by them. / /inimiimiiimmmmm imwa 
a. From coloring matter, chloro- AAlllMhlsP!!"^ MmM -^'S- 123. 
phyl, contained within the cells the 
leaf exhibits its rich green, and the 
corolla its various hues ; but cellular tissue is in itself transparent. 
b. The organical cells of plants appear to be the seats of the various changes 
which constitute the functions of nutrition and reproduction. In cellular plants no 
other tissue is ever formed. They absorb nourishment through their membranes, 
and produce new individuals by the secretions they elaborate. In the newly 
formed tissue of vascular plants there is only cellular tissue. 
c. Crystals are found within the cellules of some plants ; they are of different 
sizes and forms ; some have the appearance of bundles of fine needles, and from 
this cause the term raphides (from the Greek raphis, a needle) has been given to 
the whole class, though now they are found to be variously formed. Raphides are 
found in liliaceous plants, in the squill, in the sepals of the strawberry, and in the 
Turkey rhubarb, in which they exist as the oxalate of lime. 
The Cellular tissue composes the pith, parenchyma, and 
cotyledons of almost all vegetables. It is abundant in tubers, 
116. Vegetable tissue.— 117. ^ sUular tissue— o. Ohloropliyl— 6. Functions of o«Us-"C. R..phide9 
Cellular tissue, where found 1 
