tioned. The improved sap, like the vivid arterial blood, then proceeds to nourish and invigorate the whole frame. I very much doubt, however, if those who suggested the above hypothesis, could have given so satisfactory an explanation of it.
That the secretions of plants are wonderfully constant appears from the operation of grafting. This consists in uniting the branches of two or more separate trees, as Dr. Hope's willows, see p. 60, and a whole row of Lime-trees in the garden of New College, Oxford, whose branches thus make a network. This is called grafting by approach. A more common practice, called budding, or inoculating, is to insert a bud of one tree, accompanied by a portion of its bark, into the bark of another, and the tree which is thus engrafted upon is called the stock. By this mode different kinds of fruits, as apples, pears, plums, &c., each of which is only a variety accidentally raised from seed, but no further perpetuated in the same manner, are multiplied, buds of the kind wanted to be propagated being engrafted on so many stocks of a wild nature. The mechanical part of
