to Mr. Livingstone, that air made dry by means of sulphuric acid might be advantageously employed for this purpose, and he says that the success of his experiments was complete. He placed the seeds to be dried in the pans of Leslie's ice machine, and carefully replaced the receiver without exhausting the air; small seeds were sufficiently dried in one or two days, and the largest seeds in less than a week. (Hort. Trans., iii. 184.)

Other contrivances might easily be adopted. Muriate of lime, for instance, which has the property of absorbing the moisture of the atmosphere, might, perhaps, be employed with advantage in drying the air in which seeds are placed after being gathered.

The reason why it is so important that seeds which have to be long kept should be thoroughly dried is, partly because seeds have the power of decomposing water, which causes the commencement of germination (14.), and, if this happens while they are cut off from the other means of existence, the process of growth must be stopped, and their death will follow; and, in part, from the tendency of vegetable matter in contact with water to putrefy, if the actions of life are not in play.

CHAP. VII.

OF SEED-PACKING.

IT seldom happens that seeds are sown as soon as they are ripe; it is sometimes desirable that they should be preserved for long periods of time; the power of conveying them for great distances, through various climates, is one of those upon which man most depends for the improvement of the horticultural resources of all countries; and for this purpose large sums are annually expended, both by governments and individuals. It is, therefore, an object of the first importance to ascertain what is not well understood, as it would seem, namely, the causes by which the destruction of the germinating power of seeds is effected; for it is only by doing this, that their preservation can be secured.

Seeds are probably possessed of different powers of life, some preserving their vital principle through centuries of time, while others have but an ephemeral existence under any circumstances. The reasons for this difference are unknown to us, and apparently depend upon a first cause, over which we have, therefore, no control; but the fact of great longevity in some seeds is certain, and there seems no reason why the conditions which

enable them to preserve their germinating power for long periods of time should not be discovered and imitated.

Without admitting such doubtful cases as those of seeds preserved in mummies having germinated, there are many instances of seminal longevity about which there can be no doubt. Books contain an abundance of instances of plants having suddenly sprung up from the soil obtained from deep excavations, where the seeds must be supposed to have been buried for ages. Professor Henslow says that in the fens of Cambridgeshire, after the surface has been drained and the soil ploughed, large crops of white and black mustard invariably appear. Miller mentions a case of Plantago Psyllium having sprung from the soil of an ancient ditch which was emptied at Chelsea, although the plant had never been seen there in the memory of man. DeCandolle says that M. Gerardin succeeded in raising Kidneybeans from seed at least a hundred years old, taken out of the herbarium of Tournefort; and I have myself raised Raspberry plants from seeds found in an ancient coffin, in a barrow in Dorsetshire, which seeds, from the coins and other relics met with near them, may be estimated to have been sixteen or seventeen hundred years old.

In these cases, the only circumstances that we can conceive to have operated must have been such

a degree of dryness as prevented the decomposition of the seed on the one hand, and the excitement of its germinating powers on the other, a moderately low temperature, and in some of them the exclusion of air; for moisture, heat, and communication with the air, are necessary to enable seeds to grow (14.). The tendency of moisture exposed to the air, and in contact with inert vegetable matter, such as a torpid seed, is by degrees to produce decay, which rapidly spreads to the neighbouring parts. But, if the vitality of a seed is excited by a fitting temperature, the moisture with which it is in contact is then decomposed, the oxygen so obtained combines with the carbon of the seed, and forms carbonic acid which flies off, and by degrees reduces the amount of carbon lodged in the tissue of the seed to that which is best suited for the growth of the embryo (103.); then, if the embryo is so situated that it cannot obtain from the surrounding medium food upon which to subsist, its germination stops, and, being deprived of its carbon, the safeguard of its vitality is removed, and it perishes. If, however, the amount of moisture in contact with a seed is very small, as in the dry earth at the bottom of a tumulus for instance, the temperature at the same time low, and the access of atmospheric air cut off, neither putrefaction nor germination is likely to occur. If seeds are exposed to a high temperature in dryness, they will not perish, unless

the temperature rises beyond any thing likely to occur under natural circumstances. Edwards and Colin found that even wheat, barley, and rye, inhabitants of temperate countries, would bear when dry 104° for a long time without injury, although they died in three days in water at 95°; and a much higher prolonged temperature may be expected to produce no ill effect upon seeds inhabiting hotter countries. There is no apparent reason why the exposure of dry seeds to the air should destroy vitality, unless the exposure is very much prolonged; nor have we any evidence to show that it does, so long as they remain dry. The way in which the atmosphere would act injuriously upon dormant seeds is, by its oxygen abstracting their carbon; and it was formerly supposed that the carbonic acid extricated by germinating seeds was formed in this way. But the very valuable observations and experiments of Messrs. Edwards and Colin (See Comptes rendus de l'Académie des Sciences, vii. 922.) show that carbonic acid is formed by the assistance of the oxygen obtained by the decomposition of water.

If we apply these considerations to the plans. usually employed for preserving artificially the vitality of seeds, we shall find them offer a ready explanation of the success that attends some methods of packing, and the constant failure of others.

The great object of those who have devised means