292 



SCIENCE-GOSSIP. 



CHARACTERISTIC BRANCHING OF BRITISH FOREST-TREES. 



By the Rev. W. H. Porchas. 



(Continued from page 23S.) 



The Wych Elm or Scotch Elm. 



\Y 



'E now come to consider those trees whose 

 leaves are arranged in an alternate maimer. 

 We will take first the wych elm (Ulmus montana, 

 Linn.), as a tree in which the conditions of 

 growth are especially easy to follow. In this 

 and the other English kinds of 

 elm, we have the simplest form 

 of spiral arrangement of leaves, 

 namely, that in which they are dis- 

 tichous or two-ranked, borne alter- 

 nately on opposite sides of the stem 

 or shoot. In this arrangement, each 

 third leaf stands directly over the 

 first, the fourth over the second, 

 and so on, and since the branches 

 arise from buds formed in the axils 

 of the leaves, the branches will 

 necessarily follow the same arrange- 

 ment. The two-ranked order is 

 indeed lost or obscured in the main 

 trunk, because many of the buds 

 which are formed in the axils of the 

 leaves of the primary stem remain 

 dormant. Those buds which are 

 nearest the tip of the annual shoot 

 are generally the strongest and most 

 ready to burst into growth when the 

 spring arrives. Thus they get the 

 start of those lower down and pro- 

 duce longer and more vigorous 

 twigs, causing the others to grow 

 but feebly or even to remain dor- 

 mant, and eventually to perish 

 through lack of nourishment. 



The flowers are borne in small 

 lateral tufts, which arise immedi- 

 ately from the last years wood 

 without any accompaniment of 

 leaves; hence, when the seed has 

 fallen off, a clean scar is left, and there is no 

 farther growth from that point, there being no 

 leaves in whose axils buds for another year may 

 be formed. Thus those lengths of the branches 

 or shoots which have flowered remain ever after- 

 wards, as a general rule, leafless and unbranched. 

 After some years, however, the bark will some- 

 times become knotty, and form adventitious buds, 

 which give rise to little tufts of leaves, which give 

 a short, bushy clothing to the branch, but quite 

 unlike the normal branching. The wych elm pro- 

 duces flowers much earlier in its life than does its 

 relative, the small-leaved elm, so that the flowering- 



Spray or Wych Elm, Winter 



State. 

 j, b, leaf-buds ; c, d, flower-buds 



habit does not, as in that, affect chiefly the younger 

 spray wood, but affects also those earlier branches 

 which eventually become the main limbs of the tree. 

 This leads to the comparatively loose and open mode 

 of growth which characterizes the wych elm. 



The angle at which the branches 

 diverge from the main stem, and 

 the lesser branches from their parent 

 branches, is commonly a wide one, 

 but it varies in different individuals, 

 and is, I believe, wader in the 

 t youngest spray w T ood than in the 



earlier branchings. In the robust 

 varieties, such as constitute what I 

 will regard as the most marked and 

 characteristic form of the wych elm, 

 the leading branches ascend but 

 little and are often almost horizontal, 

 especially towards their end. As 

 leaves ordinarily present one of their 

 surfaces to the sky, the other to the 

 earth, the twigs formed in the axils 

 of those leaves spread out hori- 

 zontally on each side in a fan-like 

 manner. The branch thus keeps a 

 regular form, and the leading shoot 

 continues to maintain pretty nearly 

 its original direction ; for although, 

 as pointed out by Henfrey, in his 

 • : Elementary Course of Botany" 

 (page 35), the growing point itself 

 perishes instead of being developed 

 into a terminal bud, its office is 

 taken up by the nearest axillary bud, 

 which thus carries the branch forward 

 in the original line. In the varieties 

 which, through constitutional ten- 

 dency or through uncongenial soil and 

 surroundings, are of feebler growth, 

 as well as in such as flower very freely, it is diffe- 

 rent . In these, very few leaf -buds are formed, and 

 they are generally towards the tip of the annual 

 shoot, and of such buds no more than two, 

 or even only one, may start into growth. When 

 it does so, it seems to have the constitution rather 

 of a lateral than of a terminal bud, giving rise to a 

 shoot which diverges at a wide angle from its 

 parent shoot instead of following the same direc- 

 tion ; hence arises the gnarled or zigzag growth 

 which has been noticed by Gilpin in his " Forest 

 Scenery T ' as giving to the wych elm somewhat of 

 the character of the oak. 



