The philosophy of budding is very similar to that of grafting. The latter process is performed when the plant-life is almost dormant, and the co-apted parts are ready to take the initiative steps of vegetation, and to effect their union by means of new adventitious cells, before the free flow of sap in the growing season. Budding, on the contrary, is done in the hight of that season and toward its close, when the plants are full of well matured and highly organized sap, when the cell circulation is most active, and the union between the parts is much more immediate than in the graft; were it not so, indeed, the little shield, with its actively evaporating surface of young bark, must certainly perish from exposure to a hot dry atmosphere. The _cambium_, or gelatinous matter, which is discovered between the bark and the wood when they are separated, is a mass of organizable cells. Mr. Paxton, using the gardener's expression, calls it the "pulp." Budding is most successfully performed when this matter is abundant, for then the vitality of the tree is in greatest degree of exaltation. The individuality of the bud was sufficiently argued in the first section of this chapter, it need not now be again introduced, except as appropriately to remind us of the fact where the propagation depends upon this circumstance--the future tree must spring from the single bud which is inserted. Mr. A.T. Thomson, in his Lectures on the Elements of Botany, page 396, says:--"The individuality of buds must have been suspected as early as the discovery of the art of budding, and it is fully proved by the dissection of plants. * * Budding is founded on the fact, that the bud, which is a branch in embryo, is a distinct individual. It is essential that both the bud and the tree into which it is inserted should not only be analogous in their character, as in grafting with the scion, but both must be in a state of growth at the time the operation is performed. The union, however, depends much more upon the bud than upon the stock--the bud may be considered a centre of vitality--vegetative action commences in the bud, and extends to the stock, connecting them together."--"The vital energy, however, which commences the process of organization in the bud, is not necessarily confined to the germ, nor distinct from that which maintains the growth of the entire plant; but it is so connected with organization, that when this has proceeded a certain length, the bud may be removed from the parent and attached to another, where it will become a branch the same as if it had not been removed."