HISTOLOGY OF THE RHIZOME. 



119 



ent functions. The fundamental parenchyma is a kind of store- 

 house in which matter and energy are stored mainly in the 

 form of starch, C 6 H 10 O 5 and in which active chemical changes 

 take place. The cells are thin- walled and soft, and are rather 

 loosely joined together, leaving numerous intercellular spaces 

 (Figs. 52, 53). They contain protoplasm and a nucleus, and 

 very numerous rounded grains of starch. This starch is stored 

 up by the plant during the summer as a reserve supply of food 

 just as hibernating animals store up fat in their bodies for use 

 during the winter. Accordingly, starch increases in quantity 

 during the summer and decreases in the spring when the plant 

 resumes its growth, before the leaves are unfolded. The paren- 

 chyma probably has also the function of conducting various sub- 

 stances (especially dissolved sugar) through the plant by diffusion 

 from cell to cell. 



The sclerotic parenchyma and sclerotic prosencJiyma (Figs. 49, 50) are 

 dead, and hence play a passive part in the adult vegetal economy. The 

 former co-operates with the epidermis ; the 

 latter probably serves in part to support the 

 soft tissues, and to some extent affords a 

 channel for the conveyance of the sap. The 

 sap, however, does not flow through the 

 cavities, but passes slowly along the sub- 

 stance of the porous walls. The cells of 

 both these sclerotic tissues have very thick, 

 hard, brown walls, perforated here and 

 there by narrow canals. The cells of the 

 parenchyma are prismatic or polyhedral ; 

 those of the prosenchyma elongated, and 

 pointed at their ends. In both, the proto- 

 plasm and nuclei disappear when the cells 

 are fully formed. Towards the apical buds 

 both fade into ordinary fundamental paren- 

 chyma. 



Fibro-vascular System. The fibro- 



vascular bundles (p. 115) are long FIG. si. (After Sachs.) view of 

 strands or bands of tissue which ap- the rhizome, which is supposed 



to be transparent so as to show 



pear in CrOSS-Section as isolated Spots the network of the upper fibro- 

 (Fig. 48). The bundles are not vascular bundles. Z, a leaf. 



really isolated, however, but join one another here and there, 

 forming an open network (Fig. 51), which can only be seen in a 



