104 



HISTORY OP THE VEGETABLE KINGDOM. 



six in taxodium disticlnim; eight in pinus stro- 

 his; and lastly, ten and even twelve in /'!«2«s 

 pinea. 



It is thus seen that the number of cotyledons 

 is not the same in all plants, and that the divi- 

 sion into monocotyledons and dicotyledons, if 

 strictly observed, is incapable of including all 

 knovifn vegetables. Besides, it not unfrequently 

 happens, that the two cotyledons unite and ad- 

 here together, so that, at first sight, it is difficult 

 to say whether an embryo is monocotyledonous 

 or dicotyledonous, as, for example, in the horse- 

 chestnut. 



The cotyledons appear to be destined by nature 

 to favour the development of the young plant, 

 by supplying it with the first materials of its 

 nutrition. For this purpose, the cotyledons are 

 almost always very thick and fleshy, in plants 

 which have no etidospenn, whereas they are thin, 

 and as it were leafy, in those which are furnished 

 with that organ. These differences may easily 

 be seen on comparing the thickness of the cotyle- 

 dons in the kidney-bean and the ricinus com- 

 munis. 



At the period of germination, the cotyledons 

 sometimes remain concealed under ground, with- 

 out appearing at the surface. In this case, they 

 bear the name of liypogeal cotyledons, as in the 

 horse-chestnut. At other times they emerge 



a Oj cotyledons, forminf^ seminal leaves ; b, the gemmule ex- 

 panded into primordial leaves; e, tlie radicle. 



from the ground, in consequence of the elonga- 

 tion of the neck, which separates them from the 

 radicle. In this case, they are named epigeal, 

 as in the kidney-bean and most of the dicotyle- 

 dones. When the two cotyledons are epigeal, 

 or rise above the ground, they form the two 

 seminal leaves. 



The gemmule is the simple or compound body 

 which arises between the cotyledons, or in the 

 very cavity of the cotyledon when the embryo 

 has only onf . It was formerly called the plu- 

 tnule. Aa this organ, in most cases, bears no 



similarity to a feather which it was thus supposed 

 to resemble, "but, on the other hand, always 

 forms the first bud (gemma) of the young 

 plant which is about to be developed, the name 

 gemmule is more suitable. The gemmule is the 

 rudiment of all the parts which are to be devel- 

 oped in the open air. It is formed of several 

 small leaves variously folded upon themselves, 

 which, being developed by germination, become 

 the primordial leaves. Sometimes it is free, and 

 to be seen at the exterior, previous to germina- 

 tion. At other times, on the contrary, it becomes 

 apparent only when gennination has commenced. 

 Lastly, in some rare cases, it is concealed under 

 a kind of envelope which is named coleoptile. 

 This envelope of the radicle is, in most cases, to 

 be considered only as a thin cotyledon, covering 

 the gemmule in the manner of a sheath. 



The caidicle. This organ is not always very 

 obvious. It is confounded, on the one hand, 

 with the base of the cotyledonary body, and on 

 the other with the radicle, of which it is a kind 

 of prolongation. It is by the growth which the 

 caulicle acquires during germination, that the 

 cotjledons, in some plants, are raised out of the 

 ground. 



As the monocotyledonous embryo and the 

 dicotyledonous embryo differ greatly from each 

 other, in the number, form, and arrangement of 

 the parts which enter into their composition, we 

 shall give a separate account of the characters 

 peculiar to each. 



The dicotyledonous embryo, or that which has 

 two distinct lobes, presents the following char- 

 acters : Its radicle is cylindrical or conical, naked, 

 and projecting. It elongates at germination, and 

 becomes the true root of the plant. Its two 

 cotyledons are attached at the same height upon 

 the caulicle ; they have, in many cases, a thick- 

 ness proportionate to the thinness of the endo- 

 sperm, or its total absence. The gemmule is 

 contained between the two cotyledons, which 

 cover it, and, in a great degree, conceal it. The 

 caulicle is more or less developed. 



Such are the characters common to the dico- 

 tyledonous embryos in general. Some of them, 

 however, present anomalies which might at first 

 seem to remove them from this class. Thus the 

 two cotyledons are sometimes so intimately 

 united, as to look like a single one ; as in the 

 horse-chestnut, and usually in the chestnut. 

 But it will be remarked that this union is merely 

 accidental, for in some cases it does not take 

 place. Besides, every embryo, the base of the 

 cotyledonary body of which is entirely cleft, or 

 divided into two, although it should itself appear 

 simple and undivided at its summit, is to be con- 

 sidered as truly dicotyledonous. 



The monocotyledonous embryo is that which, 

 previous to germination, is perfectly undivided, 

 and has no cleft or incision. If in most cases. 



