324 On the Buds and Rainificailom of Plajiisr 



aqueous humour, \vhich is the ascending sap. The liler^ 

 alburmim, medullary sheath, and sometimes the tubes of 

 the bark, are the only organs which nature employs in the 

 '•otyledons to convey the sap to the ramification.- of the 

 trunk. But after the sheath has produced the prclonga- 

 tions^or germs of the buds, the liber and alburnum secure 

 ia preference the preservation of the individual; for, when 

 the new production of these orojans is prevented, the plant 

 infallibly dies : on the other hand, if nature destroys the 

 sheath, the tree very often vegetates as before; and to be 

 fully convinced of it we need only mention the enormous 

 boabab of the coast of Africa. Besides, the ingenious ex- 

 periments of Mirbel have fully shown how, bv^the help of 

 the pores and fissures with which almost all the tubes 

 atid cells of vegetables are pierced, the sap may be conveyed 

 to all the parts ; and how nature, to convey the juice from 

 one organ to the other, may find ways which to us appear 

 extraordinary. Hence we are obliged to believe, that in the 

 case v.here the sheath does not exist, or a graft has suc- 

 ceeded, and where the pith is converted into wood, the 

 prolongations may receive the nourishing liquor with which 

 they are filled, from the living tissue with which thcv are iu 

 immediate contact. In plants, even the interior part of 

 which is very sound, the sap cannot be conveyed imme- 

 diately from the tubes of the sheath of a trunk to those of 

 the sheath of an old branch. In this case, the prolonga- 

 tions are not composed of tubes; thev have become entirely 

 ligneous, and their vessels, changed into fibres, no longer 

 convey the juices. There is no longer any organic com- 

 niunication but by means of the ulhiirnvm, the liber, the 

 medullary radii, and the bark : even the latter rarely serves 

 for conveying the sap. It thence follows, that the sap of 

 the trunk ascends in the sheath, passes thence into the 

 liber, or the alburnum, to be conveyed to the sheath of the 

 branch through the cellular and vascular tissue. When it 

 reaches the sheath of the branch, it is conveyed to the fol- 

 lowing ran)ification in the same manner as from the trunk 

 to the principal branch. 



The origin of buds, of which I have spoken, enables us 

 to conceive the cause* of the firm insertion of the branch 

 into the trunk. The bud has been produced by a prolonga- 

 tion of the medullary sheath : the first stratum of the wood 

 is formed while that bud has been elongated into a branch : 

 the trunk has produced one at the same time; the ligneous 

 zones have sijcceedcd regularly from year to year in the 

 trunk and in the branches, and each zone of the branches 



is 



