42 SYLVA AMERICANA. 



always situated between it and the embryo, and yet is constantly 

 distinct from the former. In the natural order of grasses the 

 part under consideration forms a scale between the embryo and 

 the albumen. 



The true use of the vitellus is supposed to be to perform the 

 functions of a cotyledon with regard to air, if not to light, till a 

 real leaf can be sent forth, and the subterraneous cotyledons of 

 Gaertner in the horse chesnut and garden nasturtium are rather 

 of the nature of a vitellus. It does not appear that any plant 

 with genuine ascending cotyledons is likewise furnished with this 

 organ ; on the other hand, it commonly belongs to such as have 

 the most copious albumen, and therefore should seem to answer 

 some other end than mere nutriment, which is supplied by the 

 latter. 



We learn from the above inquiries, that the old distinction 

 between plants with one cotyledon and those with several may 

 still be relied on, though hi the former the part which has 

 commonly been so denominated is the albumen, as in corn, the 

 real cotyledon of which is the scale or vitellus, which last organ 

 however seems wanting in palms, lilies, &c, such having really 

 no cotyledon at all, nor any thing that'can perform its office, 

 except the stalk of the embryo. In the horse chesnut, oak and 

 walnut possibly, whose seed lobes do not ascend, the functions 

 of a real cotyledon, as far as air is concerned, and those of the 

 albumen may be united in these lobes, as is the case with most 

 leguminous plants ; which is rendered more probable, as several 

 of the latter have the corresponding parts likewise remaining 

 under ground. 



The testa, or skin, contains all the parts of a seed above 

 described, giving them their due shape ; for the skin is perfectly 

 formed, while they are but a homogeneous liquid. This coat 

 differs in thickness and texture in different plants. It is some- 

 times single, but more frequently lined with a finer and a very 

 delicate film called by Gaertner membrana, as may be seen in a 

 walnut, and the kernel of a peach, almond, or plum. In the 

 jasmine a quantity of pulp is lodged between the membrana and 

 the testa, constituting a pulpy seed, semen baccatwn, which is 



