102 



PHYSIOLOGICAL VIE"WS. 



almost destitute of any kind of sensation, and yet they are ranked among animal 

 substances. 



116. The vegetable substance consists of parts, called by the 

 general name tissue^ divided into Cellular and Yascular. 

 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 menibrane 2Xi^ fiber. The 

 membrane forms ovoid cells (Fig. 

 122, a), while the fiber is elongated 

 into tubes ipcd). 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 cZ, Fig. 122, 

 show the cells, seen at a becoming vascular). 



11 T. Cellular tissue. Parenchyma, 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, 



a. From coloring matter, chloro- 

 i)hi/l, contained within the cells the 

 leaf exliibits its rich green, and the 

 corolla its various hues ; but cellular tissue is in itself transparent. • 



6. 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 witliin 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, 



123. 



116. Vegetable tissue.— 117. Cellular tissue— fl. Chlorophyl— J. Functions of cells- c. Raphides 

 Cellular tissue, where found 1 



