SECRETED FLUIDS. 87 



tioned. The improved sap, like the vivid 

 arterial blood, then proceeds to nourish and 

 invigorate the whole frame, I verv much 

 doubt, however, if those who suggested the 

 above hypothesis, could have given so satis- 

 factory an explanation of it. 



That the secretions of plants are wonder- 

 fully constant appears from the operation of 

 grafting. This consists in uniting the branches 

 of two or more separate trees, as Dr. Hope's 

 Willows, seep. GO, and a whole row of Lime- 

 trees in the garden of New College, Oxibrd, 

 whose branches thus make a network. This is 

 called grafting by approach. A more com- 

 mon practice, called budding, or inoculat- 

 ing, is to insert a bud of one tree, accom- 

 panied by a portion of its bark, into the bark 

 of another, and the tree which is thus engraft- 

 ed upon is called the stock. By tliis mode 

 different kinds of fruits, as apples, pears, 

 plums, <Scc., each of which is only a variety 

 accidentally raised from seed, but no further 

 perpetuated in the same manner, are multi- 

 plied, buds of the kind wanted to be propa- 

 gatied being engrafted on so many stocks 

 of a wild nature. The mechanical part of 



