OF THE SEED AND GERMINATION. 



105 



it is easy enough to distinguish, in the dicotyle- 

 donous embryo, the diflferent parts of which it 

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

 tyledonous embryo, in which all its pai-ts 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 embryo, the radicular body 

 occupies one of its extremities. It is more or 

 less rounded, often has very httle prominence, 

 and forms a kind of indistinct papilla. At other 

 times, on the contrary, it is extremely broad and 

 flat, and forms the greatest part of the mass of 

 the embryo, as in most of the gi-aminese. 



Tlie radicle is contained in a coleorhiza, which 

 it bursts at the period of germination. It is not 

 always simple, as in the dicotyledones, but is 

 commonly formed of several radicular filaments, 

 which sometimes separately perforate the cole- 

 orhiza which contains them, as in the graminese. 

 The cotyledonary 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 all 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 sheath closed on aU 

 sides, which embraces and covers the rest. The 

 caulicle does not generally exist, or is intimately 

 confounded with the cotyledon or the radicle. 



Such is the more usual organization of the 

 monocotyledonous embryos; but, in many cir- 

 cumstances, there occur modifications peculiar 

 to certain plants. Thus, for example, the family 

 of the graminese presents some peculiarities in 

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

 two parts : the first a thick fleshy body, applied 

 upon the endospenn; the second, the hlastus, 

 which is the one to be developed. 



The term germination is applied to the series 

 of phenomena through which a seed passes, when 

 having arrived at a state of maturity, and being 

 placed in favourable circumstances, it swells, 

 bursts its envelopes, and tends to develope the 

 embryo which it contains. Before a seed can 

 germinate, there must be a concurrence of cir- 

 cumstances favourable and essential to this pro- 

 cess. 



The seed must be in a state of maturity, must 

 have been fecundated, must contain an embryo 

 perfect in aU 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 leguminose. Thus, kidney-beans have ger- 



minated after having been kept for sixty years ; 

 and some seeds of the sensitive-plant are said to 

 have perfectly geiminated about a hundred 

 years after they were gathered. But, before 

 seeds that have been long kept can germinate, 

 they must liave been defended against the con- 

 tact of ah', light, and moisture. 



The external agents which are essential to 

 germination are water, heat, and au\ 



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 ahmentary substance that it acts in 

 this case ; its solvent faculty, and . its fluidity, 

 qualify it to become a menstruum 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 natm-e 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 means 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 be 

 too great, otherwise the seeds would undergo a 

 kind of maceration, which would destroy then 

 germinative faculty, and prevent their develop- 

 ment. We here speak of the seeds of land 

 plants, for those of aquatic vegetables germinate 

 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 vehicle 

 to the substances which form 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 under 

 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 will dry 

 them up and destroy their vital principle. Thus 

 a heat of from 45° to 60° of the centigrade ther- 

 mometer prevents germination, while a heat not 

 higher from 25° to 30°, especially if accompanied 

 o 



