36 NORMAL HRANCHING [CH. 



Taking the simplest and commonest cases first. Or- 

 dinary branches arise in the axils of the leaves, by the 

 elongation of the buds, and themselves bear leaves with 

 axillary buds, as we have seen. Consequently, as regards 

 position, the branches follow the same rules as the buds, 

 and if every leaf-axil developed its normal bud and 

 subsequent branch, we should have the branching per- 

 fectly regular, a case never realised though some approach 

 to it occurs in a few instances, e.g. young Maples, Horse- 

 chestnuts, &c. with opposite branches, and Apples, Poplars, 

 &c. with alternate branching. 



If the primary axis goes on growing in length and 

 developes branches — secondary axes — in normal suc- 

 cession, so that the youngest and shortest are nearest 

 the growing point, on the flanks of which all normal 

 appendages arise in the first instance, we find the whole 

 branch-system tapering, and the order of succession of 

 the branches is said to be acropetal. This case is well 

 illustrated by young and vigorously growing Pines, 

 Spruces, Silver Firs, &c. If each branch so produced 

 grows on nornially, the whole may result in very regular 

 figures, whether a branch arises in most or only in a few 

 of the leaf-axils, e.g. many Conifers and young flowering 

 plants generally ; but it is obvious that accidents of 

 various kinds — e.g. breakages by wind or snow, injuries 

 by insects or other animals, &c. — may stop the de- 

 velopment of one or more branches at any age from its 

 bud-state onwards, and at once introduce disturbances in 

 the symmetry. It is owing to such causes that older 

 trees are never regulai', and the same applies to the root- 

 system, the symmetrical development of which is inter- 

 fered with by various exigences met with in the soil, such 

 as mechanical obstacles, dry patches, clay, injuries by 

 in.sects, &c. 



