CUCURBITA 607 



first leaf. After a week, as many as six leaves may be differen- 

 tiated, but the entire structure is still small and enclosed by the 

 bases of the two cotyledons. (Fig. 309, D.) In about two weeks, 

 the first leaf expands, being diverged at right angles to the plane 

 of the cotyledons. 



The bundle supplying the first leaf usually anastomoses with 

 one or two branches of the cotyledonary trace; and the other 

 epicotyledonary traces are later differentiated against the trans- 

 verse bundles of the cotyledonary plate. The number of bundles 

 and their arrangement in the first internode are variable; but in 

 the second and third internodes, the two cycles of bundles are 

 established which characterize the upper internodes. 



The Bicollateral Bundle. — Since Hartig (15) described the 

 occurrence of inner phloem in C. Pepo in 1854, there have been 

 many investigations of the vascular relationships that exist in 

 the Cucurbitaceae. Because differences in the interpretation of 

 the phloem have arisen, a brief summation of the divergent views 

 is here included. De Bary (3) originated the term "bicollateral" 

 to apply to vascular bundles which have 



"two groups of phloem one being situated ... on the outside of the 

 xylem and a second on its inner side." 



He pointed out that 



"both groups of phloem have the typical structure . . . and are espe- 

 cially remarkable for the size of their sieve tubes. They are frequently 

 connected by means of a narrow band, fringing the lateral edge of the 

 bundle, and containing some sieve tubes, so that in these cases the 

 bundle, strictly speaking, belongs to the concentric type." (Fi-. 

 315.5.) 



Herail (17) agreed with de Bary, interpreting the bundle as 

 truly bicollateral, since he found the development of all three 

 parts — outer phloem, xylem, inner phloem — to be synchronous. 

 Von Faber (9) concluded that both the inner and outer phloem 

 were similar in structure, arising from a single procambial strand, 

 and regarded the term "bicollateral" as accurately describing the 

 bundle. 



On the other hand, Lamounette (2.5) thought that the inner 

 phloem developed subsequently to the outer, being formed by the 

 activity of parenchymatous cells in the medulla. He observed no 

 inter-connection between the two and advocated the abandonment 



