84,0 On the Buds and IRamifications sf Plants. 



from that ot the trunk, when the medullary canal of that 

 part is filled v^iih ligneous strata, which is the case in se- 

 veral bushes and shrubs where an interior liber is formed 

 annually of the pith, until the canal whicli contains it has 

 altogether disappeared, as in the ash, the oak, shumac, 

 &c. ; but it is principally in the latter that we may be con- 

 vinced that it i;; never by the medullary sheath, nor by the 

 interior cambium, that these internal zones are produced. 



The increase in length oi buds and t\\ igs is ascribed to 

 an erection of the tubes of the liber. If the bark of a 

 young branch be separated as far as the terminal bud in a 

 young poplar, for example, and particularly before winter, 

 or in the tollowing spring, it will be found that the inner 

 bark has never become lengthened. The upper part of a 

 branch and a flower-bud is formed only by the pith, the 

 medullary sheath, and the bark. I think I may conclude 

 from this observation, that the increase of the stems or 

 trunks, and the ramifications, depends merely on the 

 elongation of the vessels of the medullary sheath.. The 

 alburnum^ the tubes of which have ti direction perfectly 

 straight, presents itself at the upper part of a branch under 

 the form of separate fibres, which lose themselves at the 

 surface of the medullary sheath. This observation explains 

 to us also why iiie zones of the upper part of a branch are 

 in number inferior to those of the base. It confirms also 

 what I have said in regard to the birth of buds ; for, if we 

 examine the bud of a small brancli in any tree whatever, 

 we shall be convinced that it is the medullary sheath with- 

 out exception that composes alone I he interior of that 

 organ. 



Explanation of the Jiaures hlomring to the alove article'. 

 See Plate III. 



Fig. 1, A vertical section of a piece of a branch of 

 shumac. 



A, The bark. 



B, Ligneous zone of one year. 



C, The medullary sheath. 



D, A bud. 



E, The s\velled-up part of the bark at the base of the 

 bud. 



F, Herbaceous prolongation of the medullary sheath, 

 •-\vhich has traversed the wood and given birth to the bud, 



G, The pith. 



Fig. 2, 



