ATTACHMENT OF BRANCHES. 275 



If the young branch he now dissected, it is found 

 to possess exactly the same structure as the stem in 

 in the early stage of its growth ; that is, to consist of 

 a central pith turgid with fluid, surrounded by the me- 

 dullary sheath, around which the spiral vessels ap- 

 pear in distinct longitudinal bundles ; and beyond them 

 a layer of semi-organized alburnum, bounded by the 

 liber ; the vascular fasces of the bark are imbedded in 

 the cellular integument, and the whole inclosed by the 

 epidermis, which at this period is generally covered 

 with excretory glands or some kind of pubescence. 

 But after the leaves have expanded and performed 

 their functions for some time, if the branch be again 

 examined, by carrying a longitudinal section into the 

 stem, we perceive its alburnum, now fully organized, 

 and continuous with the new layer in the stem, depos- 

 ited over that of the former year, which has already 

 become wood ; and, as the branch increases annually 

 by new layers, in the same manner as the stem, a si- 

 mitar section made at any subsequent period displays 

 its connexion with the stem, forming a cone, the apex 

 of which touches the medullary sheath of the stem, 

 and the base its surface whence the branch projects. 



Such are the appearances which mark the origin of 

 the branch and its connexion with the trunk, in the 

 Lilac ; and the same, with some modification, are 

 perceptible in all ligneous dicotyledons. 



We have seen that the rudiment of the bud is per- 

 ceptible, in the axill of the leaf, on the young branch 

 at the moment of its protrusion from the bud in early 

 spring ; and, that at this period, at least, it is an isolat- 

 ed body, distinct, as Gsertner has correctly asserted, 

 from the proper and permanent members of the plant. 

 The question thence occurs, — When and how are 

 buds formed? Du Hamel supposed that they originate 

 in what he terms pre-organized germs, which are de- 



