GERMINATION, or BUDDING. The process by which a plant is produced from a seed. The phenomena of germi nation are best observed in dicotyledo nous seeds ; such, for instance, as the bean,, lupin, &e. These seeds con sist of two lobes or cotyledons, enveloped in a common membrane ; when this is removed a small projecting body is seen, which is that part of the germ which af terwards becomes the root, and is termed the radicle : the other portion of the germ is seen on carefully separating the cotyledons, and is termed the plinnula ; it afterwards forms the stem and leaves. When the ripe seed is removed from the parent plant it gradually dries, and may be kept often for an indefinite period without undergoing any change ; but if placed under circumstances favorable to its germination, it soon begins to grow : these requisite circumstances are a due temperature, moisture, and the presence of air. The most favorable temperature is between 60° and 80° ; at the freezing point none of the more perfect seeds vegetate ; and at temperatures above 100°, the young germ is usually injured. No seed will grow without moisture : water is at first absorbed by the pores of the external covering, and decomposed ; the seed gradually swells, its membranes burst, and the germ expands. The root is at first most rapidly developed, the materials for its growth being derived from the cotyledons ; and when it shoots out its fibres or rootlets, these absorb nourishment from the soil, and the pin mule is developed, rising upwards in a contrary direction to the root, and ex panding into stem and leaves. For this growth thepresence of air is requisite; if it be carefully excluded, though there be beat and moisture, yet the seed will not vegetate. Hence it is that seeds buried very deep in the earth, or in a stiff clay, remain inert ; but, on admis sion of air by turning up the soil, begin to shoot forth. From experiments which have been made upon the gfirmination of seeds in confined atmospheres, it ap pears that the oxygen set free by the de composition of water combines with a portion of the carbon of the seed, and carries it off in the form of carbonic acid, and that the consequence of this is the conversion of part of the albumen and starch of the cotyledons into gum and sugar ; so that most seeds, as we see in the conversion of barley into malt, be come sweet during germination. Light is injurious to the growth of a seed. It is, therefore, obvious that the different requisites for germination are attained by placing a seed under the surface of the soil warmed by the sun's rays, when it is moistened by its humidity and by occasional showers: excluded from light, but within reach of the access of air.
When the young plant is perfected, the cotyledons, if not coverted into leaves, rot away, and the process of nu trition is carried on by the root and ieaves : the principal nourishment is taken up from the soil by the root, and chiefly by its small and extreme fibres ; so that when these are injured or torn, as by careless transplantation, the plant or tree generally dies. The matters ab sorbed, consisting of water holding small portions of saline substances, and of or ganic matter in solution, become the sap of the plant ; and this is propelled up wards in the vessels of the stein, or of the outer layer of wood, into the leaves ; hero it is exposed to the agency of air, or of light : it transpires moisture, and oc casionally carbonic acid. But the leaves also at times absorb moisture, and dur ing the influence of light they decom pose the carbonic acid, and, retaining the carbon, evolve oxygen ; the sap thus becomes modified in its composition, and the characteristic proximate principles of the vegetable are formed. These return in appropriate vessels from the leaves, chiefly to the inner bark, where we ac cordingly find the accumulation of the peculiar products of the plant : they also enable it annually to form a new layer of wood. Hence it is that the transverse sectica. of the wood exhibits as many dis tinct zones as the tree is years old. We are ignorant of the causes of this circula tion of the sap; . but that it does follow the cause which has been stated is proved by the operation which gardeners call ringing, and which they sometimes re sort to, to make a barren branch bear flowers and fruit : it consists in cutting out and removing a circular ring of bark, so as to prevent the return of the sap by the descending vessels, which at first ooze copiously, but afterwards the wound heals, and the juices are accumulated in all parts above the extirpated ring, pro ducing tumefaction in the limb, and often inducing a crop of flowers and fruit, or causing those to appear earlier than on the uncut branches. If a tree be wound ed so as to cut into the central portions of the wood, or the outer layer of new wood, the flow of ascending sap is then seen to take place upon the lower sec tion, where the vessels are that carry it up to the leaves • and the flow of de scending sap is principally confined to the upper section of the inner bark, from which, after a time, new bark is pro duced, and the parts again united.