Buds and Stems. 



49 



known as the primary cortex, extending to and including 

 the row of cells, b, which is termed the starch sheath or 

 endodermis. The groups of tissues within the endodermis 

 make up the central cylinder or stele. The groups of tis- 

 sues, d, which are disposed in the form of an interrupted 

 concentric zone, are known as the vascular bundles. The 

 tissues between the en- 

 dodermis and the vas- 

 cular bundles constitute B 

 the pericycle, c. The 

 tissue surrounded by -S'^f^ 

 the vascular bundles is ~^*^ " 

 termed the pith, e. The 

 tissue connecting the 

 pith with the pericycle, 

 and accordingly run- 

 ning radially between 

 the vascular bundles, is 

 termed the medullary 

 rays, f. 



In the sections of 

 Aristolochia which are 

 treated with phloroglu- 

 cin and chlor-zinc- 

 iodide,it is seen that the 



vascular bundles consist of two distinct parts — • an inner 

 part which is colored red by the phloroglucin, and possesses 

 relatively large openings, and an outer part which is col- 

 ored purple by the chlor-zinc-iodide, and whose cells are 

 relatively small. The inner part, which is known as the 

 xylent, is the water-conducting part of the bundle; while 

 the outer part, termed the phloem, is the food-conducting 

 part. The small, brick-shaped, thin-walled cells, g, be- 



FlG. 19. 



Cross section of a one-year-oJd stem of Aristolo- 

 chia, (Z, epidermis; ^, endodermis; c, peri- 

 cycle ; d, vascular bundle ; e, pith ; g, cam- 

 bium ; h. sclerenchyma ring of the pericycle ; 

 i, collenchyma ; f, medullary ray. 



