PISUM SATIVUM 363 



primordia except the enclosing sepals. (Fig. 183, C, D.) It 

 arises as an open crescentic structure with its abaxial surface 

 directed toward the keel of the flower. (Fig. 183, G, H.) Thus, 

 the young carpel develops as an open sporophyll whose edges later 

 coalesce, becoming united so intimately that the original suture 

 can only be detected with difficulty in the mature ovary, and may 

 be completely obliterated. (Fig. 183, Z.) This type of develop- 

 ment has been described by all the investigators cited above with 

 the exception of Gregoire who has stated that in Lathyrus there is 

 no distinct line between the carpellary margins at any time. It 

 seems doubtful, in the light of other work, that this can be the 

 case; and Bugnon, studying the same genus, has found it to be in 

 agreement with the development reported above. 



Vascular Anatomy of the Flower. — Moore (19, 2.6) has in- 

 vestigated the vascular anatomy of the flower in a number of the 

 papilionaceous legumes, dividing the species studied into two 

 major series based upon the number of cycles of traces which supply 

 the perianth and the androecium. He places Pisum in the "di- 

 hiate" series, under the Lathyrus type in which two cycles of 

 traces supply the perianth and androecium, and "the gaps of the 

 perianth traces extend into the departing stamen traces making 

 the stamen traces appear double in origin." Moore's account of 

 this type agrees in its major details with that given below, the 

 chief difference being in the ultimate branching of the traces sup- 

 plying the petals. 



In a transection of the pedicel of a very young flower slightly 

 below the receptacle, the vascular tissue forms a partially dissected 

 siphonostele in which several distinct vascular strands may be 

 differentiated in the provascular ring. (Fig. 184, A.') Slightly 

 above this level and below the floral node from which the calyx 

 primordia arise, 10 perianth traces diverge obliquely from the 

 vascular ring. (Fig. 184, B.) This is followed by the divergence 

 of the stamen traces from the vascular ring, and three primary 

 carpellary traces are finally differentiated from it. (Fig. 184, C, D.) 

 The branching of the perianth traces occurs just below the nodes 

 from which the petals diverge, and alternate perianth bundles 

 incline inward, forming the principal veins of the five petals. At 

 this point of inward differentiation, each petal trace gives off two 

 lateral branches which continue upward and become the right and 

 left lateral calyx bundles of the adjacent sepals. The median bun- 



