CUCURBITA 605 



together with the two on each lateral face, make up the basic 

 number of 10 bundles. Frequently, an additional one is formed 

 on each side of the oval by the branching of one or the other of 

 the lateral bundles. (Fig. 315, A.') The bundles so derived 

 continue up the axis to the cotyledonary node; but any of them 

 may give rise to one or more additional bundles, this being espe- 

 cially true of those located at the ends of the oval. (Fig. 313, 

 /-M.) 



The Cotyledonary Node. — At the cotyledonary node, the 

 divergence of the cotyledons results in the formation of a compli- 

 cated vascular pattern which, like that of the hypocotyl, may 

 show many variations. About 3 or 4 mm. below the node, the 

 middle bundle at each end of the oval divides into two parts which 

 separate and anastomose with adjacent lateral bundles. These 

 continue in a tangential course until each end bundle anastomoses 

 with its respective adjacent central bundle, reducing the number 

 of bundles to four, two in the center of each broad side of the 

 hypocotyl. (Fig. 313, N.) The upward continuations of these 

 four bundles connect with the traces of the cotyledons. The four 

 traces continue upward and outward into the broad bases of the 

 cotyledons; but before the divergence of the cotyledons is complete, 

 each trace branches laterally so that a single vascular bundle 

 differentiates toward the margin of the cotyledon. (Fig. 313, 0.) 

 From this lateral vein, four or more large veins diverge upward, 

 and the two median traces also continue into the cotyledon where 

 they may anastomose to form a single median vein or remain 

 distinct. Thus, the vascular system of each cotyledon consists 

 of at least nine principal vascular bundles. (Fig. 313, P.) 



An inner or adaxial phloem is present in the veins; and, in the 

 larger ones, connective phloem is also differentiated. Along 

 the adaxial surface of the vascular bundles there are zones of 

 collenchyma, and the mesophyll is 15 or more cell layers in thick- 

 ness. The three adaxial ones form a closely arranged palisade 

 region, and the remaining ix or more comprise the spongy paren- 

 chyma, which has some intercellular spaces. The cells of the 

 upper epidermis are somewhat larger than those of the lower and 

 may develop multicellular hairs, while the lower surface is glabrous. 

 Stomata occur in both surfaces with about equal frequency, Yasuda 

 (41) reporting 114 per sq. mm. in the upper, and 153 in the lower 

 for C. Pepo. 



