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VENTILATION BY DRAINS.

believe, of the celebrated George Stephenson, effected thus the ventilation of a vinery heated by hot-water. Underground drains were sunk, 3 feet deep, at right angles to the front wall, and extending from its inside to a walk about 12 feet distant from the house, and parallel with it. At each end of the drains was a perpendicular shaft; that in the inside opened immediately behind and below the hot-water pipes, and was never closed; that in the open air was closed by a moveable square plug. So long as the plug remained in its place no ventilation took place. As soon as the plug was removed, the denser external air pressed down into the shaft, and, rushing through the drain, delivered itself among the hot-water pipes, expanding rapidly in the house, and dispersing itself among the plants. The drains being always damp, on account of their depth in the moist heavy clay of Drayton Manor, the air which passed through them was always charged with as much moisture as was required. When the author saw this apparatus at work, some years since, its action was all that could be desired; and it would appear, from the following communication, made to the Gardeners' Chronicle, of January 28, 1854, that the merit of the plan is recognised in the neighbourhood:-"I beg to add my testimony to the advantages of underground drains for admitting air constantly to plants, especially in such weather as we have lately had, when other means of aëration must have been but limited. The plan adopted here is different from that at Drayton Manor; one large pipe is laid 3 feet deep, beginning at 90 feet from the front flues; it is carried to within 15 feet of the intended openings in the house, where three small pipes are cemented with their ends inside the larger one, one giving air in the middle of the house, the two others at equal distances on either side. It was inconvenient to bring the drain in front of the house, consequently it begins at the back, and is carried under the floor of the potting-shed and the house itself to the front flues. Besides the advantage of furnishing air at all times, the drains materially assist in keeping out frost; taking, for instance, the morning of January 3, when the thermometer was at 4°, I firmly believe that the plants would have been frozen, had it not been for the air admitted at the temperature of the earth three feet deep. I should prefer the plan employed at Drayton Manor, where the drains are in front, and each drain entire throughout. The late Mr. Milne (once gardener at Drayton) told me that the drains exceeded his most sanguine expectations, as indeed the health of his plants abundantly testified. I should mention that the heating apparatus in the house above alluded to is very small-quite insufficient for such extreme cold as that on the night of January 2. On stopping the drains on cold nights, the temperature of the house has been lower than on similar nights when the drains have been open, the external temperature in both cases being the same.-T. Dowell, Amington Hall."

CHAPTER V.

OF SEED-SOWING.

WHEN a seed is committed to the earth, it undergoes certain chemical changes before it can develope new parts and grow. These changes are brought about by heat and water, assisted by the absence of light. In many seeds the vital principle is so strong, that to scatter them upon the soil, and to cover them slightly with earth, is sufficient to insure their speedy germination; but in others the power of growth will only manifest itself under more favourable conditions: it is, therefore, necessary to consider well upon what the circumstances most suitable to germination depend.

Moisture is necessary, but not an unlimited quantity. If a seed is thrown into water and exposed to a proper temperature, the act of germination will take place: but, unless the plant is an aquatic, it will speedily perish; no doubt because its powers of respiration are impeded, and it is unable to decompose the water it absorbs, which collects in its cavities and becomes putrid. There must, therefore, be some amount of water, which to the dormant as well as the vegetating plant is naturally more suitable than any other; and experience shows that quantity to be just so much as the particles of earth can retain around and among them by the mere force of attraction. To this is to be ascribed the advantage derived from those mixtures of peat, loam, and sand, which gardeners prefer for their seedlings; the peat and sand together keep asunder the particles of loam which would otherwise adhere and prevent the percolation of water; the loam retains moisture

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DEPTH AT WHICH TO SOW SEEDS.

with force enough to prevent its passing off too quickly through the wide interstices of sand and peat.

If, during the delicate action of germination, the changes that the seed undergoes take place without interruption, the young plant makes its appearance in a healthy state; but, if by irregular variations of heat, light, and moisture, the progress of germination is sometimes accelerated and sometimes stopped, the unstable forces upon which vitality depends may become so much deranged as to be no longer able to act, and the seed will die. It is for the purpose of securing uniformity in these respects, that we employ, in delicate cases, the steady heat of a gentle hot-bed, shaded; and, in other cases, the assistance of a coating of earth scattered over the seed.

Under what depth of earth seed should be buried must always be judged of by the experience of the gardener: but it should be obvious that minute seeds, whose powers of growth must be feeble in proportion to their size, will bear only a very slight covering; while others, of a larger size and more vigour, will be capable, when their vital powers are once put in action, of upheaving considerable weights of soil. As, however, the extent of this power is usually uncertain, the judicious gardener will take care to employ, for a covering, no more earth than is really necessary to preserve around his seeds the requisite degree of darkness and moisture. An erroneous opinion is not uncommonly entertained, that seeds must be "well" buried in order that the young plants, when produced, may have "sufficient hold of the ground." But a seed, when it begins to grow, plunges its roots downwards and throws its stem upwards from a common point, which is the seed itself; and, consequently, all the space that intervenes between the surface of the soil and the seed is occupied by the base of the stem, and not by roots. This is well illustrated by the germination of such seeds as those of the Araucaria, which always grow best when merely laid on the surface of the soil with a little earth raised round their edges.

The finest Oaks spring from acorns dropped in the forest and covered by a few leaves. The Sycamore, the Ash, the

EVILS OF DEEP SOWING.

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Beech, the Horse Chesnut will all sow themselves wherever their seeds can stick to the ground until a coverlet of leaves is moistened by an April shower and warmed by an April sun. Neither have such seeds any difficulty in steadying themselves by their roots; a fang is driven by vital impulse into the earth, as in the Araucaria, and it is to that, and not to the buried

b

Fig. XXXIII.-Germination of Araucaria imbricata; a, the seed after it has inserted its radicle in the soil, the stem leaves just appearing; b, the same seed at a later period firmly fixed in the ground by its root.

neck of the stem, that the seedling trusts for support and nourishment.

It is not a little remarkable that not only do seeds germinate unwillingly if buried too deep, but that although they may grow they cannot, even if forest trees, develope with vigour for many years. It is for the purpose of placing seeds in the most favourable condition as regards air, light, and moisture, that when very small they are merely scattered upon the surface of the soil, and covered with a coating of straw or moss, which may be removed when the young seedlings are found to have established themselves. Inverting a garden pot over seeds in the open ground is practised for the same purpose. In other cases very minute seeds are mixed with sand before they are

sown.

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TEMPERATURE OF SOIL IMPORTANT.

The latter practice is not, however, merely for the sake of covering the seed with the smallest possible quantity of soil, but has for its object the separation of seeds to such a distance, that when they germinate they may not choke up each other. If seedlings, like other plants, are placed so near together that they either exhaust the soil of its organizable matter, or overshadow each other so as to hinder the requisite quantity of light, some will die in order that the remainder may live; and this, in the case of rare seeds, should, of course, be guarded against very carefully.

"The injuriousness of covering seed with too much earth arises less from the superincumbent pressure of the soil, than from the exclusion of atmospheric air, which is quite indispensable to germination. The seed of the common Flax comes up at different periods, according as it is planted in one, two, or three inches depth of soil; if it be sown four inches below the surface it will not come up at all. Not that air does not penetrate to this depth in the soil, but the quantity of air will very much depend on the looser or denser character of the soil. Thouin, in his Cours d' Agriculture, remarks that small seeds should be covered only a line deep with earth, and this spread over very loosely; seeds of the size of Peas and Beans, about three-quarters of an inch deep, and the bulky seeds of our fruit-trees, such as the Apricot, Nuts, Peaches, Almonds, with from two to three inches of soil."— German Translation.

With regard to the temperature to which a seed should be subjected, in order to secure its germination, this, undoubtedly, varies with different species, and depends upon their peculiar habits, and the temperature of the climate of which they are native. So far as general rules can be given upon such a subject, it may be stated that the temperature of the earth most favourable for germination is 50° to 55° for the seeds of cold countries, 60° to 65° for those of "greenhouse plants," and 70° to 80° for those of the torrid zone. We are assured by Mr. Cowan, that although the Cocoa-nut is cultivated in the mountainous parts of Jamaica; where the atmospheric temperature varies from 60° to 90°, it only assumes the characteristic grandeur of Palms, and can only be propagated with certainty, by the seaside, where the heat of the soil exceeds 120°. And it may be laid down as a rule, in sowing tropical

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