and such a state must also be favourable to the developement of all those secretions upon which the organisation of flowers, the setting of fruit, and the elaboration of colour, odour, flavour, &c., so much depend. Some suggestions by Mr. Knight, as to the manner in which this result can be artificially produced, will be found in the Hort. Trans., vol. iv. p. 2. and 3.; but the subject has as yet attracted little attention. (See also Hort. Trans., new series, i. 34.) CHAP. V. OF SEED-SOWING. WHEN a seed is committed to the earth, it undergoes certain chemical changes (14.) 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, are sufficient to insure their speedy germination; but in others the power of growth will only manifest itself under very 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 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 fragile machinery upon which vitality depends may become so much de ranged as to be no longer able to perform its actions, and the seed will die. It is for the It is for the purpose of securing uniformity in these respects, that we employ, in delicate cases, the steady heat of a gentle hotbed, shaded; and, in all cases whatever, 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 a 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.* Hence the common practices of sow *It may, perhaps, be as well to notice, in this place, an erroneous opinion, not uncommonly entertained, that seeds must be "well" buried in order that the young plants, when produced, may have "sufficient hold of the ground." The fact is, that a seed, when it begins to grow, plunges its root 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. ing small seeds upon the surface of the soil, and covering them with a coating of moss, which may be removed when the young seedlings are found to have established themselves. In other cases very minute seeds are mixed with sand before they are sown. 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 organisable 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. 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 coun. tries, 60° to 65° for those of "greenhouse plants," and 70° to 80° for those of the torrid zone. No seed, however, has been known to refuse to germinate in the last-mentioned temperature, although those to which such a heat is necessary will not, in general, grow in a healthy manner in a lower temperature. We have no exact experiments upon this subject, except in a few cases recorded by Messrs. Edwards and Colin, by whom there is a very valuable set of observations upon the temperatures borne by certain agricultural seeds (Annales des Sciences, new series, vol. v. p. 5.), the result of which may be thus stated: At 44-6, Wheat, Barley, and Rye could germinate. # 95°, in water, for three days, of the Wheat and Rye, and all the Barley, were killed. 104°, in sand and earth, the same seeds sustained the tem. 113°, under the same circumstances, most of them perished. ditto ditto But it was found that, for short periods of time, a much higher temperature could be borne. At 143-6°, in vapour, Wheat, Barley, Kidneybeans, and Flax retained their vitality for a quarter of an hour; but in 27 minutes, the three last died at a temperature of 125.6°. 167°, in vapour, they all perished. 167°, in dry air, they sustained no injury. It will be presently seen that some seeds will bear a much higher temperature. The foregoing observations apply to seeds in a |