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EFFECT OF DEOXYDISING SEED.

to observe the effects on seeds of acetic, nitric, and sulphuric acids, and also of water rendered alkaline by potash and ammonia. "In the alkaline the seeds vegetated in thirty hours, and were well developed in forty; while in the acetic and sulphuric they took seven days; and, even after a month, they had not begun to grow in the acetic." This experiment led to others upon lime; "a very easily procured alkali, and which he inferred to be more efficient than any other from the well known affinity of quick or newly slacked lime for carbonic acid. Lime, as taken from the quarry, consists of carbonate of lime, or lime united to carbonic acid; but, in the act of burning, the carbonic acid is driven off; and hence the great affinity of newly slacked lime for carbonic acid. He depended, therefore, upon this affinity to extract the carbon from the starch, assisted by moisture;" (Gard. Mag., xiv. 74) and he reported that the results were exceedingly striking. Old Spruce Fir seed, which would scarcely germinate at two years old, produced a fine healthy crop when three years old, having been first damped and then mixed with newly slacked lime; and, under the same treatment, an average crop of healthy plants was obtained when the seed was four years old. The manner in which the original experiments upon acids and alkalies were conducted is not explained; it is to be presumed that the water employed was only acidulated with the acids spoken of. It is, however, certain that whatever effect may be practically experienced when particular solutions are employed it has no relation to electrical action. Mr. Edward Solly proved experimentally in the garden of the Horticultural Society that electricity has no discoverable influence upon vegetation either in its active growth or during the period of germination. (See Journal of Hort. Soc. vol. i., p. 81, and ii., p. 45.)

The last method of promoting germination, to which it is necessary to advert, is the mixing seeds with agents that have the power of liberating oxygen. It has been shown that a seed cannot germinate until the carbon with which it is loaded is to a considerable extent removed; the removal of this principle is effected by converting it into carbonic acid, for which purpose a large supply of oxygen is required. Under ordinary circum

INUTILITY OF SEED-STEEPING.

237

stances, the oxygen is furnished by the decomposition of water by the vital forces of the seed; but when those forces are languid, it has been proposed to supply oxygen by some other means. Humboldt employed a dilute solution of chlorine, which has a powerful tendency to decompose water, and set oxygen at liberty, and, it is said, with great success. Oxalic acid has also been used for the same purpose. Mr. Otto, of Berlin, states that he employs oxalic acid to make old seeds germinate. The seeds are put into a bottle filled with oxalic acid, and remain there till the germination is observable, which generally takes place in from twenty-four to forty-eight hours, when the seeds are taken out, and sown in the usual manner. Another way is to wet a woollen cloth with oxalic acid, on which the seeds are put, and it is then folded up and kept in a stove; by this method small and hard seeds will germinate equally as well as in the bottle. Also very small seeds are sown in pots and placed in a hotbed; and oxalic acid, much diluted, is applied twice or thrice a day till they begin to grow. Particular care must be taken to remove the seeds out of the acid as soon as the least vegetation is observable. Mr. Otto found that by this means seeds which were from twenty to forty years old grew, while the same sort, sown in the usual manner, did not grow at all (Gard. Mag., viii. 196): and it is asserted by Dr. Hamilton (Ib., x. 368, 453,) and others, that they have found decided advantages from the employment of this substance. Theoretically it would seem that the effects described ought to be produced, but general experience does not confirm them; and it may be conceived that the rapid abstraction of carbon, by the presence of an unnaturally large quantity of oxygen, may produce effects as injurious to the health of the seed, as its too slow destruction in consequence of the languor of the vital principle.

It is an old assertion, revived within the last few years, that certain agents have a powerful action not only upon the germinating seed, but upon plants in their after growth, and that marvellous crops have been obtained by mere SEED-STEEPING, in certain solutions, without other aid. A German, of the name of Bickes, has more especially made himself conspicuous for the enthusiasm with which he has propagated this opinion. That he laboured under some delusion, is, however,

238

DURABILITY OF SEED-LIFE-COLOURED LIGHT.

certain; for no such results as those he speaks of can be obtained. (See Journal of the Hort. Soc., vol. ii. p. 35.) The subject has been treated with great care by Professor Edward Solly, whose experiments are recorded in the Transactions of the Hort. Soc., 2nd series, vol. iii. p. 197. Not only did he fail to discover any practical advantage in steeping seeds in chemical solutions, but upon the whole his results showed it to be injurious; and in no one instance did it appear that the effect of the steeping went beyond the period of germination. The trial of Bickes' method equally failed in the Jardin des Plantes, as we learn from the Revue Horticole.

The length of time that some seeds will lie in the ground, under circumstances favourable to germination, without growing, is very remarkable, and inexplicable upon any known principle. If the Hawthorn be sown immediately after the seeds are ripe, a part will appear as plants the next spring; a larger number the second year; and stragglers, sometimes in considerable numbers, even in the third and fourth seasons. Seeds of the genera Ribes, Berberis, and Pæonia have a similar habit. M. Savi is related by De Candolle to have had, for more than ten years, a crop of Tobacco from one original sowing; the young plants having been destroyed yearly, without being allowed to form their seed. This matter does not, perhaps, concern the theory of horticulture, for theory is incapable of explaining it; but it is a fact that it is useful to know, because it may prevent still living seeds from being thrown away, under the idea that, as they did not grow the first year, they will never grow at all.

Mr. Hunt believes that coloured light exercises a peculiar influence upon germination; that yellow light prevents it, and red light impedes it, while blue light accelerates it in a remarkable degree. But when seeds have been made to germinate beneath red, yellow, and blue plates of glass, no other result has been practically obtained than what may be referred to the action of bright light on the one hand, and shade on the other. If under blue glass seeds germinate more quickly than under red or yellow, it seems to be because they are much more shaded. At all events Mr. Hunt's ingenious inquiries into the effect of coloured light on plants seem to have no practical bearing.

CHAPTER VI.

OF SEED-SAVING.

THE maturation of the seed, being a vital action indispensable to the perpetuation of a species, is, in wild plants, guarded from interruption by so many wise precautions, that no artificial assistance is required in the process; but in gardens, where plants are often enfeebled by domestication, or exposed to conditions very different from those to which they are subject in their natural state, the seed often refuses to ripen, or even to commence the formation of an embryo. In such cases, the skill of gardeners must aid the workings of nature, and art has to effect that which the failing powers of a plant are unable to bring about of themselves.

Sterility is a common malady of cultivated plants; the finer varieties of fruit, and all double and highly cultivated flowers, being more frequently barren than fertile. This arises from several different causes.

The most common cause of sterility is an unnatural development of some organ in the vicinity of the seed, which attracts to itself the organizable matter that would otherwise be applicable to the support of the seed. Of this the Pear, the Pine-apple, and the Plantain are illustrative instances. The nutrition which is intended for the seed is applied to the enlargement of the fleshy part of such fruits, and the seeds are starved. The more delicate varieties of Pear, such as the Gansel's Bergamot and the Chaumontelle, have rarely any seeds; of Pine-apple, none, except the Enville now and then, have seeds, and that variety, though a large one, is of little

240

CAUSE OF STERILITY.

value for its delicacy, and probably approaches nearly to the wild state of the plant; of Plantains few, except the wild and crabbed sorts, are seedful. The remedy for this appears to be, the withholding from such plants all the sources from which their succulence can be encouraged. If, in consequence of any predisposition to form succulent tissue (on which the excellence of fruit much depends), the organizable matter of the plant be once diverted from feeding the seed to those parts in which the succulence exists, it will continue, by the action of endosmose, to be attracted thither more powerfully than to any other part, and the effect of this will be the abortion of the seed but a scanty supply of food, an unhealthy condition of the plant itself, or withholding the usual quantity of water, will all check the tendency to luxuriance, and therefore will favour the developement of the seed, whose feeble attracting force is, in that case, not so likely to be overcome by the accumulation of attracting power in the neighbouring parts. Thus we see that Pine-apples are more frequently seedful under bad cultivation, than in highly kept and skilfully managed pineries. Abstraction of branches, in the neighbourhood of fruit, has also been occasionally found favourable to the formation of seed; evidently because the food that would have been conveyed into the branches, having no outlet, is forced into the fruit, and thus reaches the seed.

Another cause of sterility is the deficiency of pollen in the anthers of a given plant, as in vegetable mules, which usually partake of the spermatic debility so well known in similar cases in the animal kingdom. It has often been found that sterility of this kind is cured by the application, to the seedless plant, of the vigorous pollen of another less debilitated variety.

In some plants, such as Pelargoniums, when cultivated, the anthers shed their pollen before the stigma is ready to receive its influence, and thus sterility results. All such cases are provided for, by employing the pollen of another flower. (See Sweet in the Gardener's Magazine, vii. 206.)

An unfavourable state of the atmosphere obstructs the action of pollen, and thus produces sterility. Pollen will not