GOSSYPIUM 



4^5 



About 2. cm. above the soil level, the xylem of each of the four 

 original transition bundles consists of two rows of spiral elements 

 and two lateral metaxylem arms. (Fig. iiy, A.') The cambium 

 is active and there is considerable secondary thickening which 

 results in the differentiation of secondary xylem adjacent to the 



Fig. 117. A-D, successive stages showing transition in upper hypocotyl : en, endodermis ; 

 wx, metaxylem ; /)f/, pericycle; /^A, phloem; />/, pith ; /;.v, protoxylem. (After Spieth.) 



tangential rows of metaxylem. Secondary phloem is laid down 

 centrifugally, the endodermis and the pericycle maintaining their 

 continuity by anticlinal divisions. The cortex is composed of 

 fifteen or more concentric layers of cells, and lysigenous canals may 

 develop in the outer portion of this region. 



At approximately 4 cm. above the level where transition is 

 initiated, the separation of each bundle into two units is com- 

 pleted. Except over the protoxylem points, where the tissue 



