[Chap. XXVIII TISSUES AND PROCESSES OF STEMS 283 



which conduction of food may take place and in which starch frequently 

 accumulates. 



sieve plate 



comparvion cell 



phloem pareacKymacell 



sieve tube 



Fig. 104. Types of cells in the phloem of a gourd stem. 



In the phloem of many vascular plants, except ferns, some gymno- 

 sperms, and most herbs, there are sclerenchyma cells, known as phloem 

 fibers, comparable to the fibers of the pericycle. These libers may occur 

 in bands, as hollow cylinders surrounding softer tissue, singly, or irregu- 

 larly. The commercially important fiber, jute, is obtained from the phloem 

 of the jute plant. The individual phloem fiber is a long, tapering cell, 

 usually with lignified walls. Short thick-walled cells, called stone cells, 

 may occur in the phloem eitlier associated with the fibers or alone. In a 



