EMARGINATE COTYLEDONS 45 



distinct petioles, 5 -nerved, with two lateral, subopposite 

 branches from the midrib some distance below the apex. The 

 plumule and radicle are small. The cotyledons gradually 

 increase in size and grow over the process in which the 

 radicle (a) lies, extending to the apex of the seed, doubling 

 over and abutting against the ridge formed by the raphe and 



FIG. 87. Convolvulus Soldanella. A, embryo, x 2. B, section of seed after 

 removal of the dorsal surface, embryo, and endosperm, x 2. C, side view of 

 ditto, x2. 



chalaza (6), and thus becoming more and more emarginate at 

 the apex. The notch is therefore due to their continuing to 

 grow at the sides after their apex has reached this ridge. 



In Ipomcea purpurea (fig. 88, A-C), where the seed is con- 

 structed generally on the same model as in Convolvulus 



FIG. 88. Ipomcea purpurea. A, embryo, x 2. B, section of seed after 

 removal of dorsal surface, embryo, and endosperm, x 2. C, side view of 

 ditto, x2. 



Soldanella, the ridge formed by the raphe and chalaza (fig. 

 88, B and C, b), is more prominent, and consequently the 

 notch of the cotyledon is deeper. Lastly, in Ipomcea dasy- 

 sperma (fig. 89, A-C) the projecting ridge of the chalaza is 

 still more developed and reaches nearly to the process which 

 supports the radicle ; the cotyledons are thus precluded from 



