PROSENCHYMATOllS TISSUE 



25S 



them the protosplasra strands extend, as shown m the 

 figure. 



414. PROSENCHYMATOUS TISSUE. — Several elongated 

 and strong tissues, which greatly strengthen the stems in 

 which they are found, are 

 collectively known as pros- 

 enchyma. The cells of 

 these tissues become much 

 thickened by the addition 

 of layers to the inner sur- 

 face, and finally lose their 

 protoplasm. They may, at 

 times, serve as store-rooms 

 for starch and other nu- 

 trients, and take an im- 

 portant part in the trans- 

 fer of the plant juices. 

 Some writers call this 

 group of tissues scleren- 

 chyma. 



415. There are four 

 main varieties of tissues {3||illl^l~^ 

 which may be included 

 under proseuchyma. (1) 

 Fibrous tissue, composed 

 of very thick -walled cells 

 with very small central 

 3a vities. F, Fig. 401. 

 They are very long and tapering at the ends, which lap. 

 Sucli tissue is found in man^^ plants where it often 

 wholly or in part surrounds the fibro-vascular bundles. 

 It is more often but not always found near the soft 

 bast: hence the cells are sometimes called hast fibers or 

 iiiird bast. (2) Wood tissue, or wood fibers. This is 

 composed of cells much like the preceding in structure. 



3'J7. Biist-tissue. s, s, sieve tubes; c, com- 

 IJunion cell ; p, shows a top view of u 

 sieve phite, with a fonipaiiion cell, c. at 

 the side; o, shows sieve plates in the 

 side of the cell. In s, s, the proto- 

 plasm is shrunken from the walls liy 

 reagents. 



