SOLANUM TUBEROSUM 543 



tissue. The abaxial (outer) phloem forms a nearly continuous 

 band on the abaxial side of the procambium. 



As the leaf matures, the cells of the procambial strand lying 

 between the abaxial phloem and the primary xylem form a cambium 

 which later gives rise to secondary vascular elements. (Fig. 

 i88, B.) In the mature leaf, both the abaxial and adaxial phloem 

 groups are distinct; but, in the principal veins, these may be 

 continuous around the flanks so that the bundle is essentially 

 amphicribral. The lateral veins resemble the midvein, but the 

 size and number of the phloem groups gradually decrease in the 

 smaller ones. No adaxial phloem is differentiated in the terminal 

 veinlets, which consist of one or two spiral protoxylem elements 

 and some adjacent conducting parenchyma located on the abaxial 

 side of the protoxylem. 



Development and Vascular Anatomy of the Flower. — Floral 

 development has been studied in several genera of the Solanaceae 

 and appears to be uniform for the family. The reports of Young 

 (31) for Solanum, Augustin (3) on Capsicum, and Warner (xy) 

 for Lycopersicum are in general agreement. The flower cluster 

 is terminal, although it appears lateral in the later stages of its 

 development owing to the growth of the adjacent axillary bud 

 which forms the continuation of the vegetative axis of the plant. 

 The primordium of the flower appears as a dome-shaped enlarge- 

 ment which at first is directly in line with the main axis, and its 

 parts develop in acropetal succession. The ensuing details of 

 development are similar to those described for Lycopersicum. 

 (Chapter XVIII.) 



In the pedicel of the flower the vascular tissue constitutes a 

 more or less continuous region; but as it broadens to form the 

 receptacle of the flower, five vascular strands diverge from this 

 cylinder and incline outwardly to occupy a peripheral position. 

 These form the five principal traces of the sepals. Slightly above 

 this point of divergence the parenchymatous gaps formed by them 

 are closed and the vascular cylinder again appears to be continuous. 

 This is followed by the divergence of five bundles constituting 

 the traces to the petals that alternate with the traces to the sepals. 

 At this same level, divisions of the original sepal bundles result 

 in the formation of lateral bundles so that each sepal has from 

 three to five vascular strands. The same situation prevails in 

 connection with the bundles to the corolla, and each petal ulti- 



