METABOLIC PROCESSES IN THE PLANT. 309 



The parenchyma of the cortex and of the pith of the upper not 

 yet fully elongated part of the hypocotyl is, as can readily be 

 determined in the usual manner, very rich in starch and sugar, 

 while the quantity of these substances in the lower elongated part 



FIG. 112. Part of a transverse section of the fully extended hypocotyl of "Ricinus com- 

 munis. The longitudinal section is represented in Fig. 33. r, parenchyma of the primary 

 cortex ; m, the pith. Between r and b the single-layered vascular bundle sheath with 

 starch grains (starch sheath). The nbro-vascular bundle consists of the phloem, b, y, the 

 xylem, f, g, and the cambium, c c. The cambium, c c, is continued laterally in the ground 

 tissue between the neighbouring bundles as interf a scicular cambium, cb. In the phloem 

 are b b, bast fibres; y y, partly parenchyma, partly sieve tubes; in the xylem are 1 1, 

 narrow pitted vessels ; g g, wide pitted vessels, and between them wood fibres. (After 

 Sachs.) 



of the hypocotyl more and more diminishes. In the fully elongated 

 part of the hypocotyl, sugar and starch are wanting in the paren- 

 chyma ; starch grains are only to be detected in the cells of the 

 starch sheath surrounding the ring of vascular bundles. In the 

 tissue of the main root neither starch nor fat are now to be found. 



