STRUCTURE OF SEED. 207 



or less unequal, but they are not strictly opposite, the 

 smaller one arises a little above the larger, and, conse- 

 quently, the embryo, although having two cotyledons, 

 belongs to the class of Monocotyledons, which con- 

 firms the whole structure of the stem and fructifying 

 apparatus. 



We call those plants Acotyledons, which are devoid 

 of cotyledons ; but under this name one may comprehend 

 two very different organizations ; — 1st, The Nemea of 

 Fries, or cellular plants, which are all considered as 

 Acotyledons, although in most the germination is ill 

 understood ; — 2d, Among vascular plants, those which 

 are devoid of cotyledons, and which Fries names exclu- 

 sively Acotyledons, are generally also devoid of leaves: 

 such are Cuscuta, and Orobanche, which, notwithstand- 

 ing, we are obliged to class among Dicotyledons, and 

 perhaps some leafless Orchideae, which do not less belong 

 to Monocotyledons. The only known example of a vas- 

 cular plant furnished with leaves, and apparently devoid 

 of cotyledons, is Lecythis, the singular germination of 

 which Du Petit Thouars has described. We must con- 

 sider this seed as formed of two fleshy cotyledons, united 

 with each other and with the plumule, and which do 

 not separate at germination. In several succulent plants 

 the cotyledons are so small, as in Cactus Melocactus, 

 &c. (PI. 23, fig. 3,) or so adherent to the cauliculus, as 

 in Stapelia, that we might think them absent, from a 

 superficial observation. 



Next to their position, that which most distinguishes 

 cotyledons from each other, and which causes the great- 

 est difference in their history, is the presence or absence 

 of stomata, which is always connected with their tex- 

 ture. All those which, when developed, present stomata 

 on their surface, are more or less foliaceous, and of a 



