But we must not yet take our leave of the subject of agriculture; we have prepared the soil, it remains for us now to sow the seed. In this operation we must be careful not to bury it too deep in the ground, as the access of air is absolutely necessary to its germination; the earth must, therefore, lie loose and light over it, in order that the air may penetrate. Hence the use of ploughing and digging, harrowing and raking, &c. A certain degree of heat and moisture, such as usually takes place in the spring, is likewise necessary.
CAROLINE.
One would imagine you were going to describe the decomposition of an old plant, rather than the formation of a new one; for you have enumerated all the requisites of fermentation.
MRS. B.
Do you forget, my dear, that the young plant derives its existence from the destruction of the seed, and that it is actually by the saccharine fermentation that the latter is decomposed?
CAROLINE.
True; I wonder that I did not recollect that. The temperature and moisture required for the germination of the seed is then employed in producing the saccharine fermentation within it?
MRS. B.
Certainly. But, in order to understand the nature of germination, you should be acquainted with the different parts of which the seed is composed. The external covering or envelope contains, besides the germ of the future plant, the substance which is to constitute its first nourishment; this substance, which is called the parenchyma, consists of fecula, mucilage, and oil, as we formerly observed.
The seed is generally divided into two compartments, called lobes, or cotyledons, as is exemplified by this bean ([Plate XV.] Fig. 1.)—the dark-coloured kind of string which divides the lobes is called the radicle, as it forms the root of the plant, and it is from a contiguous substance, called plumula, which is enclosed within the lobes, that the stem arises. The figure and size of the seed depend very much upon the cotyledons; these vary in number in different seeds; some have only one, as wheat, oats, barley, and all the grasses; some have three, others six. But most seeds, as, for instance, all the varieties of beans, have two cotyledons. When the seed is buried in the earth, at any temperature above 40 degrees, it imbibes water, which softens and swells the lobes; it then absorbs oxygen, which combines with some of its carbon, and is returned in the form of carbonic acid. This loss of carbon increases the comparative proportion of hydrogen and oxygen in the seed, and excites the saccharine fermentation, by which the parenchymatous matter is converted into a kind of sweet emulsion. In this form it is carried into the radicle by vessels appropriated to that purpose; and in the mean time, the fermentation having caused the seed to burst, the cotyledons are rent asunder, the radicle strikes into the ground and becomes the root of the plant, and hence the fermented liquid is conveyed to the plumula, whose vessels have been previously distended by the heat of the fermentation. The plumula being thus swelled, as it were, by the emulsive fluid, raises itself and springs up to the surface of the earth, bearing with it the cotyledons, which, as soon as they come in contact with the air, spread themselves, and are transformed into leaves.—If we go into the garden, we shall probably find some seeds in the state which I have described—