180 VEGETABLE ORGANOGRAPHY. 



are found there are prolonged downwards ; and form 

 by their union a woody sheath, which creeps down 

 between the wood and bark of the lower part of the 

 tree, and thus forms a new woody layer, placed over 

 the former one. A bud or germ which is developed on 

 a tree, does not essentially differ, according to him, from 

 an ordinary seed : the young shoot which springs up 

 represents the plumule ; the pith plays the part of the 

 cotyledon ; and the woody fibres are the roots of the 

 bud. These roots have a tendency to descend, as those 

 of the plant itself; and, in descending, they insinuate 

 themselves into the only passage which they find per- 

 meable. 



Numerous objections have been made against this 

 theory. 1st, It is said that these roots of the buds 

 ought to be seen, at some period of the life of trees, 

 descending all along the woody body, as is said to be 

 the case in Draccena. Du Petit-Thouars has been 

 obliged, in order to answer this objection, to suppose 

 tnat this descent takes place with such rapidity as to 

 escape our notice ; he even goes so far as to compare it to 

 the swiftness of the electric spark, or of light. 2d, It is re- 

 marked that in grafted trees the wood situated below tlie 

 graft resembles that of the stock, and that above it is like 

 that of the graft : thus, when an Almond, the wood of 

 which is yellow, is grafted on a Plum, which has the 

 wood red, the wood is red below the graft, and yellow 

 above it : now it seems evident that if the wood were 

 formed by the buds, it ought, from the top to the bottom, 

 at least externally, to resemble that of the graft. Du 

 Petit-Thouars answers, that the woody fibre which 

 descends from the bud retains the nature of the graft ; 

 whilst passing under its liber it is nourished by its juice, 

 but when it arrives under the liber of the stock, this 

 furnishes it with another nourishment, which changes 



