PORTULACfLE 225 



wider end of the seed, are much wider than the terete radicle, 

 which they equal in length. They are also incumbent and lie 

 transversely to the wider plane of the seed. 



Calandrinia umbellata, C. pilosiuscula, and Spraguea 

 umbellata agree very closely with Portulaca except that the 

 seeds of Spraguea are thickest in the middle and taper to 

 each end, so that the cotyledons are narrower for the size 

 of the seed than in the type given. A more remarkable excep- 

 tion occurs in Claytonia perfoliata (fig. 204), the embryo of 

 which lies in the broader plane of the seed. The cotyledons 

 are nevertheless very narrow, linear, plano-convex, and ac- 

 cumbent, perhaps for the reason suggested on page 69. The 

 embryo seems to originate with its cotyledons in the narrow 

 plane of the seed while yet straight ; but certainly as soon as 

 it begins to curve in conformity with the outline of the seed, 

 the cotyledons lie in the broad plane with their edges to the 

 axis. When first observable with a simple lens, the embryo 

 is a small, nodular, obcordate body, but it soon becomes oblong, 

 and the cotyledons attain such a thickness as to become closely 

 adpressed to one another ; in the next stage it is cylindrical, 

 and soon after commences to curve and ultimately attains 

 a horse-shoe shape. 



Exceptions to the general rule occur in Grahamia, Tali- 

 nopsis, and sometimes in Anacampseros, where the embryo is 

 almost straight, and the seeds have only a scanty endosperm. 

 The seeds of Grahamia are also irregularly obovate, subreni- 

 forrn, very much compressed laterally, and girt with a mem- 

 branous wing ; in Talinopsis they are obovate-oblong, incurved 

 and hooked but wingless ; while in some species of Anacam- 

 pseros they are angled or compressed and three-winged, but in 

 others wingless. 



Cotyledons. As far as observed there are two distinct types 

 of cotyledons, namely, a broad and a narrow one. One of 

 the broadest types occurs in Portulaca grandiflora, notwith- 

 standing the extreme minuteness of the seeds. The cotyle- 

 dons however lie in the narrow plane of the seed, but in its 

 widest part, and they are consequently several times as wide 

 as the radicle is thick. When fully developed after germin- 

 ation they are oblong-oval, obtuse, fleshy, shortly petiolate, 



Q 



