ELEILEXTARY STRrCTTRE. 37 



(cylindrical, or prismatic. It occurs frequently in the cellular 

 I tissue of Monocotyledonous Plants. 



c. Tabular Parenchyma is that which consists of tabular 



cells. It is found in the epidermis and other external parts 



of plants {figs. 96 and 97). A variety of this kind of parenchjnna 



is called muriform, because the cells of which it is composed 



j resemble in their form and arrangement the courses of bricks 



\ in a wall {fig. 68). This variety occurs t^- go 



V in the medullary rays or the silver grain "' 



of wood. 



Such are the commoner varieties of 

 parenchyma, all of which are connected in 

 various ways by transitional forms which 

 it is unnecessary to describe here. When 



ordinarv parenchvmatous cells become ^r,,,!*'^,,^'?,!^^^!,^,,.- 

 , ' . ^, , r, - T -, Muriiorm parencnynia. 



much thickened by soft secondary de- 

 posits, as in the fronds of many Algse, &c., the tissue formed 

 by them is called by some authors collenchjma; or if the 

 secondary deposits are of bony hardness, as in the stones of 

 fruits, Henfrey has proposed the term sttrenchyma. 



It frequently happens that ordinary parenchymatous cells 

 become thickened by secondary deposits, in such a manner as to 

 form pitted cells, or some variety of fibrous cells. The combina- 

 tion of these so as to form tissues, constitute, respectively, Pitied 

 Cellular Tissue, and Fibro-ccllular Tissue. These tissues are, 

 however, but slight modifications of true parenchyma, and are 

 frequently included by authors with, the other varieties under 

 that name. 



In some of the lower orders of plants there is a kind of tissue 

 present, which is quite as distinct from parenchyma, as this is 

 from prosenchyma and the tissues formed by the vessels of 

 plants. To this the names of Tela cofifeata and T/iterlacifig fibril- 

 liforni Tissue have been given. It occurs especially in Fungi and 

 in Lichens {fig. 26), and consists of very long thread-like cells, 

 or strings of cells, simple or branched, with either thin, soft, 

 readily destructible walls, as in Fungi ; or dry and firm ones, as in 

 Lichens ; the whole inextricably interwoven or entangled with 

 each other, so as to form a loose fibrilliform tissue. 



The tissues above described constitute the entire structure of 

 the lower orders of plants, such as the Algte, Fungi, and Lichens, 

 which are hence frequently termed Cellular plants ; while those 

 orders above them, which contain commonly, in addition to cells, 

 vessels, and prosenchymatous wood-cells, are called Vascular 

 Plants (see page 9). In these higher orders of plants, paren- 

 chymatous ceils constitute all the soft and pulpy parts; and 

 in cultivating plants or parts of plants for culinary purposes 

 and for food generally, the great object aimed at is to develop 



