52 



DKSCRIPT1VE BOTANY. 



PART I. 



in fact, be considered as so many partial stems en- 

 grafted into the main trunk. Originating, as we have 

 stated, from buds, their disposition round the stem 

 must depend upon the arrangement of the leaves, to 

 which we shall allude when we treat of those organs. 

 We may, however, remark, that branches are never 

 so symmetrically arranged as leaves ; because a great 

 many buds are never developed at all. This arises 

 from the unfavourable circumstances under which many 

 are placed, for receiving a sufficiency of air, of moisture, 

 and more especially of light. The consequence is, that 

 those which originate on the lower parts of the stem, are 

 either much stunted, or become abortive. 



(60.) Development of Branches. When a branch 

 is not developed, where a bud has been formed, the 

 latter still continues to live ; and, in dicotyledonous 

 trees, is carried outward with the increasing bulk of 

 the stem, and awaits at the surface for a proper op- 

 portunity, when a sufficient quantity of light, or of 

 some other requisite, may enable it to "break" into 

 a branch. This fact is familiar to every horticul- 

 turist, and is the foundation of the principle upon which 

 he regulates the pruning of his trees. If a section of 

 the stem be made at the point where an undeveloped 

 bud is seen to protrude, it will show the course which 

 the bud has followed in passing from the centre outwards, 

 marked by a line or wake, 

 which traverses the several 

 layers (fig. 44-.). Hence, 

 branches of the same 

 age, may have origin- 

 ated from buds which 

 have been formed at very 

 different periods of the 

 tree's growth. This is 

 a further cause, tending 

 to destroy the symmetry 

 which they might other- 

 wise have exhibited in their arrangement round the axis 



