50 Thompson — The Sh-ucturc and Development of 



clearly distinguishable. In the bending out of the leaf bundles 

 into the petioles, the same crossing of the internal phloem to 

 the exterior takes place in the leaves of the seedling, that has 

 been described above for adult leaves. Scott in his work upon 

 Ipomoea versicolor found that in the hypocotyl near its junction 

 with the root, the internal phloem passed through the xylem 

 and joined the external phloem. He was thus able to prove 

 the continuity of the phloem throughout the plant. Similar 

 phenomena were observed by Gerard in different plants. There 

 is no trace of any continuity between the external and internal 

 phloem of the hypocotyl of Gelsemhan. The course of the 

 bundles throughout the hypocotyl and stem is indicated in the 

 diagrammatic figure below. 



o, origin of first pair of internal phloem patches; o', origin of second pair; co, 

 cotyledon, /•, first foliage leaf; P, second foliage leaf; P, third foliage leaf; ga^ grow- 

 ing apex, X, crossing of internal phloem to exterior. 



