CACTEJE 



short, or cylindrical and elongated. The simplest type of 

 embryo observed is that of Mamillaria longimamma. The 

 seed is obovoid, often more or less compressed laterally, and 

 its interior is entirely occupied by the embryo which conforms 

 to it. There is no separation into radicle and cotyledons, but 

 the whole forms an obovoid mass slightly narrowed at the end 

 next the hilum, which may be considered as representing the 

 radicle. The presence of cotyledons is merely indicated by a 

 shallow triangular notch at the apex. From these circum- 

 stances and from the behaviour of the seedlings after germina- 

 tion, the greater part of this thick, short and fleshy embryo 

 must be considered as the hypocotyl which has assumed a 

 succulent state, and acts as a storehouse of reserve-material 

 for the use of the young plant. More differentiation is shown 

 by Echinocactus Wislizeni. The obliquely oblong or subreni- 

 forrn seed contains a small quantity of subfarinaceous endo- 

 sperm round one end of which the cotyledons are curved or 

 bent so that the embryo presents an oblong, stout, fleshy body 

 hooked at one end. The embryo of Cereus Napoleonis (fig. 395) 

 is very similar to that of Echinocactus Wislizeni, but the 

 cotyledons are more bent, and the seed is suborbicular and 

 much compressed with a deep indentation at the hilum. The 

 walls of the testa are very unequally thickened, the greatest 

 thickening taking place round the end of the seed distant from 

 the hilum. Endosperm is wanting, and the curvature of the 

 embryo is brought about by a thickening of the testa and the 

 indentation at the hilum. In Opuntia Rafinesquii the seed is 

 reniform or suborbicular, subcompressed, and the embryo is 

 curved round the greater part of the periphery of the seed, 

 enclosing in the curve a quantity of farinaceous endosperm, 

 and greatly resembling what occurs in most of the Caryo- 

 phyllese, Phytolaccaceae, ChenopocUaceae, and other allied 

 Orders. The cotyledons are plano-convex and linear. There 

 is more complication in Qpuntia Dillenii (fig. 399), where the 

 embryo is on the whole curved, but bent or angled three times 

 transversely, enclosing a small quantity of endosperm. The 

 cotyledons are plano-convex and subulate-linear. The large 

 orbicular and compressed seed is very much thickened round 

 the periphery. 



