i 9 1 2] JONES— DI A NTH ERA g 



The buds, found at the preceding stage in the axils of the 

 cotyledons, have developed somewhat, each having now two very- 

 small leaves, each of which furnishes a single trace which passes 

 downward into the hypocotyl. These become inserted, one on 

 each side of the cotyledonary trace, between it and an arm of the 

 forked bundle entering from above. 



The bases of the first pair of leaves were at first distinct, but 

 they have by this time grown together to form a short tube. This 

 is the case with all the later formed leaves. A bud is starting to 

 develop in the axil of each of the first pair of leaves, but at this 

 stage has developed no vascular tissue. 



From now on, the order of differentiation of new bundles is the 

 same as that just described. At the close of each stage, there 

 develops a pair of opposite bundles, each double in appearance, 

 having two groups of protoxylem and protophloem elements 

 separated by a parenchymatous ray. These bundles fork below, 

 the forks being inserted between the traces of the underlying pair 

 of leaves and those of the latest formed pair. Above, the bundles 

 fork, connecting with the outgoing, latest formed leaf traces. In 

 the next stage, these bundles become surrounded by a sheath which 

 finally develops into a well marked endodermis. At the beginning 

 of each stage, there is differentiated a trace from each of the newly 

 formed leaves, which trace passes downward to the node below, 

 being there inserted in the crotch of the underlying forked bundle 

 which has just been developed at the close of the preceding stage. 



The central bundle 



The earliest sign of any medullary vascular tissue is to be 

 found in a single example of a fourth-stage seedling, where, in the 

 first epicotylar node, there are traces of medullary phloem. The 

 course and attachment of these medullary phloem strands (fig. 30) 

 are best described by starting with the conditions found just below 

 the node, and following these upward through the node. 



As the four bundles found in the basal epicotylar internode 

 spread out on entering the node to form a complete ring, three 

 protophloem elements from the peripheral vascular tissue pass 

 inward toward the center. One of these protophloems arises from 



