6 ON SEEDLINGS 



Seedlings. The form of the embryo and its parts in the 

 seed have a direct bearing upon the form of the seedling with 

 its cotyledons. We meet with cotyledons of various lengths 

 and shapes, and in some cases they may be considered as 

 absent, or at all events functionless, although morphologically 

 represented. In the seeds of Mamillaria longimamma they 

 appear as the edges of a three-cornered cleft, and in the 

 seedling of M. Goodrichii they are not more conspicuous and 

 soon become indiscernible. Similar instances are furnished 

 by Echinocactus viridescens (fig. 394) and E. Orcuttii. The 

 seedling of the first named, eleven months after sowing of 

 the seed, appears as a small obovoid body representing a 

 short fleshy turbinate hypocotyl bearing minute tooth-like 

 cotyledons, above which the short stem is even stouter, 

 leafless, and covered with small spines in tufts arranged 

 in five or six longitudinal rows. Seven months after the 

 sowing of the seeds, E. Orcuttii is similar to E. viridescens, 

 but smaller. 



The cotyledons of Echinocactus Wislizeni attain some size 

 in the seed, but after germination they become merged in the 

 succulent stem by the swelling of the latter, so that seven 

 months after sowing they appear as small triangular teeth 

 about 1 mm. long, and of the same breadth, projecting from 

 the sides of the seedling. About four months after sowing, 

 the cotyledons of Cereus tilophorus borne by the clavate 

 succulent hypocotyl were 1*25 mm. long, and 2 mm. wide. 

 Those of Cereus Napoleonis after three months were 1*5 

 mm. long, 2' 5 mm. wide, triangular and succulent. The 

 hypocotyl in this case is turbinate and very short. The 

 seeds of this species are comparatively small, and so is the 

 seedling during and after germination. Seven months after 

 sowing it is much larger, with the cotyledons about 3 mm. 

 long, and as wide. Strikingly different from all of the above 

 are the seedlings of Opuntia basilaris (fig. 398). The hypo- 

 cotyl is cylindrical or slightly compressed, but much less 

 succulent than any of the above except that of Cereus tilo- 

 phorus. The cotyledons are subulate, bluntly pointed, 

 1-5-3-5 cm. long, and after a time become disarticulated from 

 the axis. They are also of unequal lengths. Abnormal forms 



