108 
PHYSIOLOGICAL VIEWS. 
branous substance appears chiefly under two elementary forms: 
viz. 1st, that of cellular texture ; 2d, vascular texture. 
Fig. 116. 
1st. Cellular texture , (Fig. 
116, a;) this, according 
to the opinion of Mirbel, is 
composed of a mass of little 
hexagonal cells, resembling 
honey-comb. Another wri¬ 
ter* compares the appearance 
of the cellular texture to the 
froth of fermenting liquor: 
he considers that each cell is 
disconnected with the others; 
while Mirbel believes that the 
divisions of the membrane, which forms these cells, are common to 
contiguous cells. The cellular system in animals contains the fat; 
in vegetables it is generally filled with resinous, oily, or saccharine 
juices ; in some cases the cells contain air only. They are usually 
marked by small dots, (as at a, Fig. 116;) these are supposed to be 
apertures, through which fluids are transmitted from one cell to 
another. 
The cellular texture composes most of the pith, parenchyma, and 
cotyledons of almost all vegetables. It is abundant in tuberous roots, 
pulpy and fleshy fruits, and the stems of grasses, and constitutes the 
principal part of mushrooms, and other cryptogamous plants. In the 
bark of plants the cellular texture is situated under the cuticle ; it is 
filled with a juice which varies in colour in different species of plants, 
but is most commonly green ; it gives its colour to the bark, as the 
same texture under the human cuticle gives colour to the skin. The 
green colour of leaves is caused by the cellular texture, which is en¬ 
closed on both sides by the cuticle. In the pith of young plants, the 
cells are filled with watery fluids, but in older plants they are empty, , 
or only filled with air. The petals of flowers owe their beautiful 
hues to the presence of cellular texture, filled with juices, which 
refract and reflect the rays of light, in a peculiar manner. 
Vascular f texture , consists of tubes, which, like the vessels of the 
animal frame, are capable of transmitting fluids. These tubes are 
open at both ends, and are protected by a coating of cellular in¬ 
tegument; their sides are thick and almost opaque. These vessels 
extend throughout the whole plant, distributing air and other fluids 
necessary to vegetation. The vascular system of plants presents a 
variety in form, and also with respect to the functions which the 
different parts perform. 
Some are entire vessels, or without any perforation, (Fig. 116, c ;) 
these convey the proper juices of the plant, and generally contain 
oils ^nd resinous juices. 
Porous vessels exhibit many perforations, (Fig. 116, b ;) they often 
separate and again unite, changing at length into cellular integu¬ 
ment 
* Dutrochet. 
t The term vascular is derived from the Latin word vasculum, a little vessel. 
Two kind of membranes—Cellular texture—how situated—Cause of the green co¬ 
lour of plants—of the hues of petals—What does the vascular texture consist of?— 
Entire vessels —Porous vessels. 
