GERMINATION. 



GESTATION. 



and leaves. When the ripe seed is removed 

 from the parent plant it gradually dries, and 

 may be kept often for an indefinite period, 

 without undergoing any change ; but if placed 

 under circumstances favourable to its germina- 

 tion, it soon begins to grow : these requisite 

 circumstances are a due temperature, mois- 

 ture, and the presence of air. The most fa- 

 vourable temperature is between 60 and 80; 

 at the freezing point none of the most perfect 

 seeds vegetate, and at temperatures above 100 

 the young germ is usually injured. No seed 

 will grow without moisture : water is at first 

 absorbed by the pores of the external cover- 

 ing, and decomposed; the seed gradually 

 swells, its membranes burst, and the germ ex- 

 pands. The root is at first most rapidly de- 

 veloped, the materials for its growth being 

 derived from the cotyledons ; and when it 

 shoots out its fibres or rootlets, these absorb 

 nourishment from the soil, and the plumula is 

 developed, rising upwards in a contrary direc- 

 tion to the root, and expanding into stem and 

 leaves. For this growth the presence of air is 

 requisite ; if it be carefully excluded, though 

 there be heat and moisture, yet the seed will 

 not vegetate. Hence it is that seeds buried 

 very deep in the earth or in a stiff clay, remain 

 inert; but on admission of air, by turning up 

 the soil, begin to vegetate. From experiments 

 which have been made upon the germination 

 of seeds in confined atmospheres, it appears 

 that the oxygen set free by the decomposition 

 of water, combines with a portion of the car- 

 bon of the seed, and carries it off in the form 

 of carbonic acid, and that the consequence of 

 this is the conversion of part of the albumen 

 and starch of the cotyledons into gum and 

 sugar ; so that most seeds, as we see in the 

 conversion of barley into malt, become sweet 

 during germination. Light is injurious to the 

 growth of the seed. It is, therefore, obvious 

 that the different requisites for germination are 

 attained by placing a seed under the surface 

 of the soil, where, warmed by the sun's rays, 

 and moistened by the humidity of the atmo- 

 sphere, it is excluded from light, but the air has 

 access to it. 



Oxygen is an essential agent in the process 

 of germination, and without it seed will not 

 germinate, a fact which has been demonstrated 

 by placing seeds in vacua, and in nitrogen, hy- 

 drogen, and carbonic acid. But, as in animal 

 life, too much oxygen is hurtful : it abstracts 

 the carbon too rapidly, overstimulates, and 

 causes feebleness of growth to the infant plant. 



When the young plant is perfected, the coty- 

 ledons, if not converted into leaves, rot away, 

 and the process of nutrition is carried on by 

 the root and leaves: the principal nourishment 

 is taken up from the soil by the root, and chiefly 

 by its small and extreme fibres ; so that when 

 these are injured or torn, as by careless trans- 

 plantation, the plant or tree generally dies. 

 The matters absorbed, consisting of water 

 holding small portions of saline substances, 

 and of organic matter in solution, become the 

 sap of the plant ; and this is propelled upwards 

 in the vessels of the stem, or of the outer layer 

 of the wood, into the leaves ; here it is exposed 

 to the agency of air and of light ; moisture, 

 538 



and occasionally carbonic acid, is transpired. 

 But the leaves also at times absorb moisture, 

 and during the influence of light they decom- 

 pose the carbonic acid, and retaining the car- 

 bon, evolve oxygen ; the sap thus becomes 

 modified in its composition, and the charac- 

 teristic proximate principles of the vegetable 

 are formed. These return in appropriate ves- 

 sels from the leaves chiefly to the inner bark, 

 where we accordingly find the accumulation 

 of the peculiar product of the plant ; they also 

 enable it annually to form a new layer of wood. 

 Hence it is that the transverse section of the 

 wood exhibits as many distinct zones as the 

 tree is years old. We are ignorant of the 

 causes of this ascent of the sap ; but that it 

 does follow the cause which has been stated is 

 proved by the operation which gardeners call 

 ringing, and which they sometimes resort to, to 

 make a barren branch bear flowers and fruit. 

 It consists in cutting out and removing a cir- 

 cular ring of bark, so as to prevent the return 

 of the sap by the descending vessels, which at 

 first ooze copiously, but afterwards the wound 

 heals, and the juices are accumulated in all 

 parts above the extirpated ring, producing 

 tumefaction in the limb, and often inducing a 

 crop of flowers and fruit, or causing those to 

 appear earlier than on the uncut branches. 



If a tree be wounded so as to cut into the 

 central portions of the wood, or the outer layer 

 of new wood, the flow of ascending sap is 

 then seen to take place upon the lower section, 

 where the vessels are that carry it up to the 

 leaves; and the flow of descending proper 

 juice is principally confined to the upper sec- 

 tion of the inner bark, from which, after a 

 time, new bark is produced, and the parts are 

 again united. To return to the process of 

 germination, every part of the seed is not es- 

 sential, nor the whole of the parts. Kidney 

 beans will germinate with only one cotyledon: 

 and oaks, also, germinate in the same state ; 

 gourds have been robbed of the radicle and 

 also the plumule, as they shoot forth, and yet 

 germination has proceeded ; but the plants 

 produced in all these cases were small, deli- 

 cate, and never come to perfection. 



GESTATION. The gestatory term in quad- 

 rupeds is much regulated by their bulk. In 

 the elephant it is about 20 months, in the camel 

 between 11 and 12, in the mare and ass the 

 same. According to the observations of M. 

 Teissier of Paris, in 582 mares, which copu- 

 lated but once, the shortest period was 287 

 days, and the longest 419; making the extra- 

 ordinary difference of 32 days, and of 89 days 

 beyond the usual term of 11 months. The cow 

 usually brings forth in about nine months, and 

 the sheep in five. Swine usually farrow be- 

 tween the 120th and 140th day, being liable to 

 variations, influenced apparently by their size 

 and their particular breeds. In the bitch, on 

 the contrary, be she as diminutive as a kitten, 

 or as large as the boarhound, pupping occurs 

 on or about the 63d day. The cat produces 

 either on the 55th or 56th day. The true 

 causes which abridge or prolong more or less 

 the period of gestation in ihe females of quad- 

 rupeds, and of the incubation of birds, arc 

 yet unknown to us. Many persons are also 



