502. THE STRUCTURE OF ECONOMIC PLANTS 



"the internal phloem extends downwards into the hypocotyl and passes 

 out between the converging protoxylem groups of each cotyledonary 

 pair of bundles, thus joining the external phloem of the root." 



In his summary, he concludes that 



"As regards the course of the internal phloem in the transition from 

 stem to root, Ipomoea versicolor may be taken as typical of plants 

 with bicollateral bundles generally." 



Fig. 162.. A protoxylem point in lower hypocotyl of three-weeks-old seedling : ca, cam- 

 bium ; CO, cortex ; en, endodermis ; /' ^h, inner phloem ; mx, metaxylem ; ph, outer phloem ; 

 /)£■/, pericycle; ^i, pith; /»x, protoxylem ; xj i, secondary xylem. 



Lee (8) investigated the seedling anatomy of Convolvulus tri- 

 color L. , var. major, and also C. tricolor L. In regard to the former 

 he concludes that 



"The phloem is extremely small in amount and at no point can 

 internal phloem be recognized with certainty — an observation which 

 emphasizes the late appearance of this tissue noticed by other 

 observers." 



In Convolvulus tricolor, he notes frequent anastomoses of strands of 

 phloem connecting the bundles in the petiole of the cotyledon, and 



