ELEMENTARY STRUCTURE. 



29 



to form pitted cells, or some variety of fibrous cells. The 

 combination of these so as to form tissues, constitutes re- 

 spectively, Pitted Cellular Tissue, and Fibro- cellular 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 contexta and Interlacing 

 fibrilUform Tissue have been given. It occurs especially in 

 Fungi and in Lichens {fig. 10), and consists of very long 

 thread-hke 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 fibriUiform 

 tissue. 



The tissues above described constitute the entire structure 

 of the lower orders of plants, as the Algie, 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. In these higher orders of plants, parenchymatous cells 



Fig. 53. Fig. 54. Fig.^b. 



constitute all the soft and 

 pulpy parts ; and in cultivat- 

 ing plants or parts of plants 

 for culinary purposes and for 

 food generally, the great ob- 

 ject aimed at is to develope 

 this kind of tissue as much 

 as possible. Parenchyma is 

 connected by various inter- 

 mediate conditions with 

 prosenchyma, which we now 

 proceed to notice. 



2. Prosekchyma. — The 

 most perfect form of pros- 

 enchyma is that common- 

 ly termed Woody Tissue, 

 {Woody Fibre of the old 

 writers, Pleurenchyma of 

 Lindley and Meyen). 



This tissue consists of 

 very fine cells, elongated 

 and tapering to a fine point at each of their extremities, their 

 inside being much thickened by secondary deposits {fig. 53), 

 and when in contact with each other, overlapping by their 

 pointed ends, so that they are firmly compacted together and 



Fig. 53. Prosenchymatous cells. Fig. 



54. Horizontal section of prosenchy- 

 matous cells. Fig. oo. Proeenchyma- 



tous cells in combination. 



