PHYSIOLOGY. 269 



ORIGIN OF BRANCHES. 



All branches proceed from germs which were formed in 

 the young plant, though they may not appear until the tree is 

 in advanced age. Even in the bud, before it is unfolded, the 

 rudiments or germs of branches may be seen. They appear 

 in the form of minute vesicles filled with a greenish fluid 

 which do not appear to have any attachment to the surround- 

 ing parts. This fluid is enveloped in cellular tissue, which 

 contain mealy particles, perhaps farina. The effect of vege- 

 table organic power, is to add new matter to this living vesi- 

 cle, which appears to be nourished by the mealy particles. 

 The first portion of the branch that can be distinctly recog- 

 nized is the pith, surrounding which, there next appear lines, 

 which are the first traces of the spiral vessels of the future 

 branch. At this period the whole germ is a completely in- 

 sulated body, within the concentric circles of the parent tree, 

 ajld continues insulated, until its complete evolution takes 

 place, in the course of which the vessels of the tree and new 

 branch join, and form a continued series. The twig there- 

 fore which appears on the surface of an old tree, is to be re- 

 garded as having originated in the first year of the growth of 

 that part of the trunk, however old it may be. 



The progress of the new branch may Fi s- 



even be traced from the medullary portion 

 of the trunk, through the concentric layers 

 to the surface on which it appears, by a pale 

 colored streak which traverses these ligne- 

 ous circles. This is represented by Fig. 

 237, where a, is a protruding bud of the 

 future limb, and b, another, making its way 

 towards the surface, each leaving the marks 

 of its passage through the ligneous circles 

 behind it. 



As the bud protrudes to form the branch, 

 the perpendicular vessels, and ligneous 

 fibres of the part where it appears, separate to permit its pas 

 sage between them, as shown by Fig. 238. These vessels 

 afterwards meet again, and pursue a curved direction around 

 the new branch. This circumstance conspires to prove the 

 fact, that branches are distinct individuals, although attached 

 to the parent. 



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