SCIENCE-GOSSIP. 



141 



CHARACTERISTIC BRANCHING OF BRITISH FOREST-TREES. 



By the Rev. W. H. Purchas. 



QOME years ago, when giving attention to the 

 subject of leaf-arrangement in trees and 

 plants, I was led to consider that since all branches 

 originate from leaf-buds, and that these leaf-buds 

 are, in the ordinary course of things, formed only 

 in the axils of leaves, it would follow that whatever 

 be the order of arrangement of leaves on the stem 

 of any given tree or shrub, such may be expected 

 to be the arrangement of the branches of that tree 

 or shrub. In practice, however, I found that the 

 order of leaf-arrangement can rarely be traced in 

 the position of the leading branches of trees, 

 and I was accordingly led to enquire why it should 

 be thus. 



The answer to the question was soon found 

 in the fact that some only, not all, of the buds on 

 the primary stem of a young tree give rise to 

 branches, whilst others remain dormant, and that 

 thus the original order is lost. But I was led at 

 the same time to perceive that not one only, but a 

 variety of causes combine to produce the peculiar 

 mode of branching and the general features which 

 characterize our different forest-trees. I therefore 

 set myself to trace these out as well as I could. 



In this pursuit I could find little help from 

 books, and I have had to rely almost entirely 

 on my own observations continued through a 

 series of years, and, although often interrupted, 

 never wholly laid aside. As a result, my en- 

 deavour in the present paper is to trace out 

 the life-history of the different trees, so far as 

 their branching is concerned, and to show how 

 the peculiarities of their mode of branching 

 result in the general form and outline which dis- 

 tinguishes one from another and enables us to 

 recognise them even in winter. Also how depen- 

 dent upon the mode of branching is the massing of 

 foliage, and the consequent arrangement of light 

 and shadow which the artist recognises and seeks 

 to depict. Although the study of the distinctive 

 forms of tree-branching is, in the first place, a 

 matter of botanical interest, I think it may be well 

 worth the while of the painter of woodland scenery 

 to give some attention to it. It should help to- 

 wards a correct and intelligent recognition of the 

 physiognomical differences in trees, and should 

 lead to the avoiding of any such mistakes as were 

 sometimes made by the older landscape painters, 

 and which have been so unsparingly exposed by 

 Mr. Ruskin. 



First, I think it will be best to enumerate the 

 different causes so far as I have been able to 

 discover them, with just enough of illustration to 

 make clear my meaning ; and, secondly, to show 



August, 1895.— No. 18, Vol. II. 



how these causes come into play in the case of 

 different trees. 



1. Arrangement of Leaves. — First and fore- 

 most must certainly come the arrangement of 

 leaves on the stem, for, as all botanists are aware, 

 this is by no means after an irregular and 

 haphazard fashion, but is regulated by definite 

 laws. These laws are not indeed observed with 

 mathematical precision, for we must not expect to 

 find this in natural history, but laws which never- 

 theless are found to prevail in the greater number 

 of instances. Leaves, then, in our common 

 deciduous trees are placed either oppositely or 

 alternately on the stem. Opposite leaves occur in 

 the case of the ash, the sycamore and the maple, 

 and there is little variety in the arrangement. 

 Each pair of leaves, when regularly grown, stands 

 at right angles to the pairs next above and below 

 it, and buds, towards the close of the season, are 

 formed in the axils of these leaves. These buds 

 give rise in the following season to branches or 

 branchlets standing opposite to each other and at 

 right angles to those above and below them as the 

 leaves had done. This, however, is liable to be 

 interfered with by some of the buds remaining 

 dormant. 



In the case of alternate-leaved trees there is much 

 more difference of arrangement. The simplest case 

 is when the third leaf stands directly over the first, 

 two ranks of leaves and consequently of branches 

 being thus formed. We find this arrangement in 

 the lime, the elm and the beech. In all cases where 

 the leaves are solitary, and not in pairs or whorls, 

 it is found that a line drawn round the stem so as 

 to pass from leaf to leaf will describe a spiral. The 

 number of leaves which intervene between that 

 from which we start and that which begins a new 

 circuit, by standing directly over the first, is found 

 to vary in different species, although tolerably 

 constant in the same species. Thus, whilst as 

 above stated, the line connecting the bases of the 

 leaves in the lime, beech and wych-elm passes only 

 once round the stem before the third leaf is 

 reached and the circuit completed, in the oak and 

 the apple the line passes twice round the stem 

 before the leaf which stands immediately over 

 the first is reached, the number of intervening 

 leaves being in these cases five, a fresh cycle 

 beginning with the sixth leaf. It would be out of 

 place to attempt to enter further on this matter ; 

 full details may be found in any good introductory 

 work on Botany, such as Henfrey's "Elementary 

 Course" or Balfour's "Class-book of Botany," by 

 those who wish to pursue the subject. 



