io8 



NATURE 



[May 31, 1888 



influence of the ethereal whirls due to their axial rotation, 

 cause simultaneously spots on the sun and cyclones on 

 the earth. 



We fail to follow M. Weyher here, and think it would 

 have been better if he had not only hesitated, as he 

 admits he did, but decided not to publish such wild 

 speculations. His experiments are exceedingly instructive 



- 



Fig. 5. 



and suggestive, and if he can ultimately succeed in imi- 

 tating the conditions of Nature more closely, we shall 

 doubtless have an end of the theoretical polemics which 

 have hitherto retarded rather than aided the progress of 

 our knowledge of aerial motions and their causes. 



E. Douglas Archibald. 



TIMBER, AND SOME OF ITS DISEASES. 1 

 VII. 



T F we pass through a forest of oaks, beeches, pines, and 

 *■ other trees, it requires but a glance to see that various 

 natural processes are at work to reduce the number of 

 branches as the trees become older. Every tree bears 

 more buds than develop into twigs and branches, for not 

 only do some of the buds at a very early date divert the 

 food-supplies from others, and thus starve them off, but 

 they are also exposed to the attacks of insects, squirrels, 

 &c, and to dangers arising from inclement weather, and 

 from being struck by falling trees and branches, &c, and 

 many are thus destroyed. Such causes alone will account 

 in part for the irregularity of a tree, especially of a Conifer, 

 in which the buds may be developed so regularly that if 

 all came to maturity the tree would be symmetrical. But 

 that this is not the whole of the case, can be easily seen, and 

 is of course well known to every gardener and forester. 



If we remove a small branch of several years' growth 

 from an oak, for instance, it will be noticed that on the 

 twigs last formed there is a bud at the axil of every leaf ; 

 but on examining the parts developed two or three years 

 previously it is easy to convince ourselves of the existence 

 of certain small scars, above the nearly obliterated leaf- 

 scars, and to see that if a small twig projected from each 

 of these scars the symmetry of the branching might be 



1 Continued from vol. xxxvii. p. 516. 



completed. Now it is certain that buds or twigs were formed 

 at these places, and we know from careful observations 

 that they have been naturally thrown off by a process 

 analogous to the shedding of the leaves ; in other words, 

 the oak sheds some of its young branches naturally every 

 year. And many other trees do the same ; for instance, 

 the black poplar, the Scotch pine, Dammara, &c. ; in some 

 trees, indeed, and notably in the so-called swamp cypress 

 (Taxodium distichum) of North America, the habit is so 

 pronounced that it sheds most of its young branches 

 every year. 



But apart from these less obvious causes for the sup- 

 pression of branches, we notice in the forest that the 

 majority of the trees have lost their lower branches at a 

 much later date, and that in many cases the remains of 

 the proximal parts of the dead branches are sticking out 

 from the trunk like unsightly wooden horns. Some of these 

 branches may have been broken off by the fall of neighbour- 

 ing trees or large limbs ; others may have been broken by 

 the weight of snow accumulating during the winter ; others, 

 again, may have been broken by hand, or by heavy wind ; 

 and y=t others have died off, in the first place because the 

 over-bearing shade of the surrounding trees cut off the 

 access of light to their leaves, and secondly because the 

 flow of nutritive materials to them ceased, being diverted 



Fig. 21.— Portion of a tree from which a branch has been cut off close to the 

 stem. C, the cambium of the branch ; B, the cortex. 



into more profitable channels by the flourishing, growing 

 parts of the crown of leaves exposed to sunlight and air 

 above. 



The point I wish to insist upon here is that in these 

 cases of branch-breaking, however brought about, open 

 wounds are left exposed to all the vicissitudes of the 

 forest atmosphere ; if we compare the remnant of such 

 a broken branch and the scar left after the natural 

 shedding of a branch or leaf, the latter will be found 

 covered with an impervious layer of cork, a tissue which 

 keeps out damp, fungus-spores, &c, effectually. 



It is, in fact — as a matter of observation and experiment 

 — these open wounds which expose the standing timber to 

 so many dangers from the attacks of parasitic fungi ; and 

 it will be instructive to look a little more closely into the 

 matter as bearing on the question of the removal of 

 large branches from trees. 



If a fairly large branch of a tree, such as the oak, is cut 

 off close to the trunk, a surface of wood is exposed, sur- 

 rounded by a thin ring of cambium and bark (as in Figs. 

 21 and 22). We have already seen what the functions 

 of the cambium are, and it will be observed that the cut 

 edge of the cambium (C) is suddenly placed under different 

 conditions from the usual ones ; the chief change, and 

 the only one we need notice at present, is that the cam- 

 bium in the neighbourhood of the cut surface is released 



