W. B. Hemsley
The Action Of Air On Germination.—Healthy germination can only take place when seeds are within reach of the influence of the air. By this it is not intended to say that seeds must be fully exposed to the atmosphere, but it has been proved experimentally that the soil or water in which the seed is placed must contain some of the oxygen of the air, or the vital force of the embryo will not be quickened. Left to itself, the penetration of air into the soil is a slow process, but frequent digging and stirring effects the object quickly, and renews the supply of this element, besides benefitting the growing plants in other ways. Every practical gardener is aware of tho almost marvellous effects of repeated hoeing among crops, especially the Cabbage tribe.
Action Of Light On Germination.—It is assumed by many persons that light is prejudicial to germination and darkness essential to it; but most seeds appear to germinate equally as well when exposed to light as when covered up, providing always that they are kept sufficiently moist. In a natural way the only covering seeds get is a more or less thick layer of leaves, as the seeds usually fall before the leaves. Nestled among the leaves, the seed does not dry up, as it would on the bare ground, and we only imitate Nature, substituting soil for leaves usually. As a rule, it is the object of the cultivator to make the condition such that nearly all the seed germinates, and this in a general way is more easily done by burying the seed in a small depth of soil. But there are some seeds, especially small ones, that germinate more freely on the surface of the ground protected by dwarf herbage.
Stimulating Agents In Germination.—Allusion has already been made to different means of hastening the germination of seeds, such as breaking the shells, soaking in very hot water, or even boiling for a short time. There are some substances which appear to exercise a stimulating effect in the germination of seeds and the future growth of the seedlings. Camphor, a vegetable product itself, appears to possess this property in an extraordinary degree. Indeed, it has been averred that camphor has the power of revivifying seeds, or at least of causing them to germinate when ordinary treatment failed. Benjamin Smith Barton was the first to point out its action upon plants at the end of the last century; and a few years ago a Mr. Vogel, of Munich, carried out a number of experiments with camphor on old seeds. Controlling experiments were conducted simultaneously, ordinary water being employed instead of camphor water. Seed of Cress three or four years old, treated with ordinary water, germinated very imperfectly and long after sowing, while that moistened with camphor water germinated quickly; that four years old in twenty-four hours, and that three years old in seven hours. Radish seed, which is usually regarded as useless after it is three or four years old, was tried seven years old, and it germinated in four days, or in a much shorter period than good fresh seed under ordinary favourable conditions. Seed of the Pea eight years old germinated in forty hours, and many other old seeds treated with camphor water exhibited equally rapid germination. Some that would not germinate at all under ordinary treatment had their germinative force revived by camphor. Other seeds, Clover, for instance, appeared to derive no benefit from the solution of camphor; but where it acts its influence is not limited to germination, but is extended to the subsequent growth. Humboldt discovered that chlorine accelerates germination, and acts as a restorer where the vital force is almost exhausted or quite lost, so far as the usual method of treatment is concerned. This must be used in a highly diluted form; about two drops of an aqueous solution of chlorine in 2 oz. of water. Iodine and bromine are said to possess similar qualities. Acid and ammonia salts in very small quantities in the water have been found to hasten germination, but they have not the power of reviving seeds.
Other Means Of Facilitating Germination.—Under this head all the various modes of preparing different seeds for sowing would have to be considered were this a treatise on raising plants from seed. As it is, it is not out of place to direct attention to the fact that the seeds of many plants undergo, according to their nature, some process before being committed to the soil. It is, in most cases, a process of removing the pericarp or pulp from the seed by maceration, by crushing, or gradually softening by storing away in moist sand. Thus the fleshy fruits of the Hawthorn are collected in autumn, and as each fruit contains from one to three "stones," enclosing one or rarely two seeds each, it is, desirable to separate and soften the stones before sowing, otherwise the seedlings would come up very unevenly and very irregularly as to time. To effect this, the fruits are mixed up with moist sand and stored away in pits or turf-covered heaps until spring, when the "stones" readily separate from each other and open. By a similar process Teak seed, which, if sown without preparation, is usually from one to two years before it comes up, may be made to germinate, as we learn from Amery's "Notes on Forestry," in three or four weeks.