OF THE SEED AND GERMINATION. 



105 



it is easy enough to ilistinguish, in the dicotyle- 

 donous embryo, the different parts of which it 

 is composed, it is not always so in the monoco- 

 tyledonous embryo, in which all its parts are 

 often so united and confounded, as to form a 

 single mass, in which germination alone enables 

 us to distinguish any thing. For this reason, 

 the organization of the embryo of the monoco- 

 tyledons is much less perfectly known than 

 that of plants that have two cotyledons. In the 

 monocotyledonous embrj'o, the radicular body 

 occupies one of its extremities. It is more or 

 less rounded, often has very Httle prominence, 

 and fonns a kind of indistinct papilla. At other 

 times, on the contrary, it is extremely broad and 

 flat, and fonns the greatest pai't of the mass of 

 the embrj-o, as in most of the gi'aminea;. 



The radicle is contained in a coleorhiza, which 

 it bursts at the period of gei-mination. It is not 

 always simple, as m the dicotyledones, but is 

 commonly fonned of several radicular filaments, 

 which sometimes separately perforate the cole- 

 orhiza which contains them, as in the graminere. 



The cotyledonai-y body is simple, and presents 

 no incision or cleft. Its form is extremely vari- 

 able, and always lateral, with respect to the total 

 mass of the embryo. Most commonly the gem- 

 mule is contained in the interior of the cotyledon, 

 which envelopes it on a!\ sides, and forms round 

 it a kind of coleoptile. It is composed of small 

 leaves enclosing each other. The outermost 

 usually forms a kind of slieath closed on aU 

 sides, which embraces and covers the rest. The 

 caulicle does not generally exist, or is intimately 

 confounded with the cotyledon or tlie radicle. 



Such is the more usual organization of the 

 monocotyledonous embryos ; but, in many ch-- 

 cumstances, there occur modifications peculiar 

 to certain plants. Tlius, for example, the family 

 of the graminciE presents some peculiarities in 

 the stnictm-e of the embryo. It is composed of 

 two parts : the first a thick fleshy body, applied 

 upon the endosperm ; the second, the hlastus, 

 which is tlie one to be developed. 



The teiTn germination is applied to the series 

 of phenomena tluough which a seed passes, when 

 having ai-rived at a state of maturity, and being 

 placed in favourable circumstances, it swells, 

 bursts its envelopes, and tends to develojie the 

 embryo which it contains. Before a seed can 

 germinate, there must be a concun'ence of cir- 

 cumstances favourable and essential to this pro- 

 cess. 



The seed must be in a state of matui-ity, must 

 have been fecundated, must contain an embryo 

 perfect in all its parts, and must not be too old, 

 otherwise it may have lost its faculty of germina- 

 tion. There are seeds, however, which retain 

 their germinating powers for a great number of 

 years, especially those belonging to the family 

 of Ipguminostc. Thus, kidney-beans have gei-- 



minated after having been kept for sixty years ; 

 and some seeds of the sensitive-plant are said to 

 have perfectly genninated about a hundred 

 years after they were gathered. But, before 

 seeds that have been long kept can germinate, 

 they must have been defended against the con- 

 tact of air, light, and moisture. 



The external agents which are essential to 

 gcnniuation are water, heat, and air. 



Water, as we have already seen, is indispen- 

 sably necessary for producing vegetation and the 

 phenomena of nutrition in plants. It is not 

 merely as an alimentary substance that it acts in 

 this case ; its solvent faculty, and its fluidity, 

 qualify it to become a menstraum and a vehicle 

 to the substances which afford nutriment to the 

 vegetable. In germination, its action is precisely 

 the same. It penetrates into the substance of 

 the seed, softens its envelopes, causes the embryo 

 to swell, and produces changes in the nature of 

 the endosperm or cotyledons, which often render 

 them fitted for supplying the young plant witli 

 the first materials of its nutrition. It moreover 

 conveys the gaseous or solid substances which 

 are to furnish aliment to the plant which is 

 beginning to grow. It also contributes to the 

 development of the plant by moans of the de- 

 composition which it undergoes; its disunited 

 elements combine with carbon, and give rise to 

 the various principles found in plants. 



The quantity of water, however, must not bo 

 too great, otherwise the seeds would undergo a 

 kind of maceration, which would destroy their 

 germinative fi^culty, and prevent then- develop- 

 ment. We here speak of the seeds of land 

 plants, for those of aquatic vegetables gemiinate 

 when entirely immersed in water. Some of the 

 latter, however, although of such there is but a 

 very small number, ascend to the surface to ger- 

 minate there in the open air, being incapable of 

 receiving development under water. It is there- 

 fore obvious, that water has two modes of ac- 

 tion in germination. It softens the envelope of 

 the seed, and renders it more easy for the embryo 

 to burst it; and affords a solvent and a veliiclo 

 to the substances which fonn the aliment of the 

 young plant. 



Heat is not less essential to germination. For 

 it exercises a very decided influence upon all 

 the phenomena of vegetation. If a seed be put 

 in a place, the temperature of which is imder 

 zero, it exhibits no germinative action, but re- 

 mains inactive, and, as it were, torpid ; whereas 

 a gentle and regular heat greatly accelerates ger- 

 mination. The heat, however, must not exceed 

 certain limits ; for, if it does, instead of favour- 

 ing the development of the^ germs, it wiU dry 

 them up and destroy their vifjj principle. Thus 

 a heat of from 45° to 50" of the centigi-ade thei-- 

 mometer prevents gennination, while a heat not 

 higher from 25° to 00°, especially if accompanied 

 o 



