OF THE SEED AXD GEHMIN.VTION. 



107 



swelling of the scetl, and tlie softening of tlie 

 envelopes wliich cover it. These envelopes burst 

 at a period which varies in different plants. The 

 l)ursting of the episperni sometimes fakes place 

 in a manner quite irregular, as in the kidney- 

 bean and common bean ; while, at other times, 

 it takes place with a uniformity and regularity 

 which are presented by all the individuals of 

 the same species. The latter circumstance is 

 chiefly observed in seeds which are furnished 

 with an embryoieffium,a. kind of operculum or lid, 

 which separates from the episperm to allow the 

 embryo to pass ; as, for example, in the Virginian 

 spiderwort, Commclina commimis, Phwnix dac- 

 ti/lifcra, and several other monocotyledonous 

 plants. The embryo takes the name of plantule, 

 or young plant, as soon as it begins to be deve- 

 loped. Tliere are then distinguished in it two 

 extremities, which always grow in opposite di- 

 rections. One of these extremities, which is 

 fonned by the gemmule, tends upwards to the 

 region of air and light, and is named the as- 

 cending caiidex. The other, which passes deeper 

 into the earth, and thus follows a direction the 

 reveree of the first, boars the name of descending 

 caudex. It is formed by the radicular body. 

 In most cases, it is the descending caudex or the 

 ladicle, that first experiences the effects of ger- 

 mination. 



During this time, the gemmule does not re- 

 main inert and stationary. From being at first 

 concealed between the cotyledons, it lises up- 

 wards, elongates, and proceeds in the direction 

 of the suiface of the ground, when it has been 

 covered with earth. When the ascending caudex 

 licgins to be developed beneath the point of inser- 

 tion of the cotyledons, it raises them, and carries 

 them out of the ground. Cotjdedons which ex- 

 hibit this phenomenon, are then named epigeaV"' 

 They enlarge, sometimes even become thinner, 

 assume a foliaceous appearance, and are then 

 named seminal leaves. When, on the contrary, 

 the ascending caudex cohimences above the co- 

 tyledons, the latter remain concealed in the 

 ground, and, in place of acquiring any increase 

 of size, diminish, wither, and at length disappear 

 entirely. They are then named ht/pogeal coty- 

 ledons t. When the gemmule has reached the 

 open air, the leaflets of which it is composed are 

 unrolled, spread out, and presently acquire all 

 the characters of leaves, the functions of wliich 

 they speedily perform. 



The use of the episperm, or proper covering 

 of the seed, is to prevent the water, or other 

 substances in which a seed germinates, from 



I acting too directly upon the matter of which 



* From \ti. upon, above, and yn, o.arlli ; — rising 

 above the surface of the ground. 



f From I'Ti, under, and ',',, cartli; — remaining 

 under ground. ' 



the embryo is composed. It perfoiTns, in some 

 measure, the office of a sieve, through which only 

 the finest earthy molecules can pass. Du Ilamel, 

 remarked that seeds, from whicli their pi-oper 

 integument is stripped, seldom germinate, or 

 produce slender and deformed plants. 



The endosperm, which is not always present, 

 is nothing more than the residuum of the water 

 contained in the cavity of the ovule, where the 

 embryo was developed. 'J'his fluid, which Mal- 

 pighi compared to the liquor amnii, when it has 

 not been entirely absorbed during the fomiation 

 and growth of the embryo, gradually acquires 

 consistence, thickens, and at length foi-ms a solid 

 mass, in which the embryo is enclosed, or upon 

 the surface of which it is merely applied. This 

 mass is the endosperm. This is the reason why 

 that body has always an inorganic aspect. Some- 

 times all the fluid ctntained in the interior of 

 the ovule, and which has not been employed in 

 nourishing the embryo, docs not harden, part of 

 it remaining fluid, as is exemplified in the cocoa- 

 nut, which contains within its kernel a greater 

 or less quantity of a kind of mild emulsion of 

 a white colour, known by the name cocoa-milk. 



The origin and first xises of the endospemi 

 show of themselves the uses to which nature 

 has intended it to be applied in gennination, to 

 supply the young plant with its first aliment. 

 The changes which it then undergoes in its 

 chemical composition and the nature of its ele- 

 ments, render it perfectly fit for this use. In 

 some plants, however, the endosperm is so hard 

 and compact, that it requires a long period to 

 soften and be reduced to a more or less fluid 

 substance, which can be absorbed by the embryo. 

 But this phenomenon always takes place. If 

 an embryo be deprived of, or separated from, 

 the endosperm wliich accompanies it, it becomes 

 incapable of being developed. It is therefore 

 evident, that the endosperm is intimately con- 

 nected with its gi'owth. 



The cotyledons, in many cases, appear to per- 

 form functions similar to those of the endo- 

 sperm. For this reason, the celebrated naturalist 

 Bonnet called them vegetaMe mammce. If the 

 two cotyledons be removed from an embryo, it 

 fades, and ceases to receive any further develop- 

 ment. If only one be removed, it may still 

 vegetate, but only in a feeble and languishing 

 manner, like a sickly and mutilated object. It 

 is a very remai'kable fact, that a dicotyledonous 

 cnibrjo, that of the kidney-bean, for example, 

 may be sjilit and separated into two lateral parts, 

 without detriment ; for, if each jiart contain a 

 perfectly entire cotyledon, it will germinate as 

 well as an entire embrj'O, and give rise to as 

 strong and vigorous a plant. 



The great difference of structure between the 

 monocotyledonous and dicotyledonous embrj'os, 

 has a remarkable influence ui)on their peculiar 



