Dec. 29, 1887] 



NATURE 



207 



Larches growing in the lowlands, however, are apt to 

 begin their renewed growth in April, and frosted stems 

 are a common result, a point which (as the renowned 

 botanist just referred to also showed) has an important 

 bearing on that vexed question — the " larch-disease." 



The supply of oxygen to the cambium is chiefly depen- 

 dent on the supply of water from the roots, and the 

 aeration of the stem generally. The water begins to 

 ascend only when the soil is warm enough to enable the 

 root-hairs to act, and new ones to be developed, and the 

 supply of mineral salts goes hand in hand with that of 

 water. 



Now comes in the question of the sources of the organic 

 substances. There is no doubt that the cambium at first 

 takes its supply of food-materials from the stores which 

 have been laid by, in the medullary rays, &c., at the con- 

 clusion of the preceding year ; and it is known that 

 special arrangements exist in the wood and cortex to pro- 

 vide for this when the water and oxygen arrive at the seat 

 of activity. 



Assuming that all the conditions referred to are favour- 

 able, the cambium-cells become filled with water in which 

 the necessary substances are dissolved, and distended 

 (become turgid, or turgescent, as it is technically called) 

 sufficiently for growth. Speaking generally, and with 

 reference chiefly to the trunk of the tree, which yields the 

 timber, the distension of the cells is followed by growth 

 in the direction of a radius of the stem, and division 

 follows in the vertical plane, tangential to the stem. Then 

 the processes already described with reference to Fig. 5 

 repeat themselves, and the trunk of the tree grows in 

 thickness. 



Now it is obvious that the thickening of the mass of 

 timber inside the cylinder of cambium must exert pressure 

 on the cortex and bark — must distend them elasticaJly, in 

 fact — and some ingenious experiments have been made by 

 De Vries and others to show that this pressure has an 

 effect in modifying the radial diameter of the cells and 

 vessels formed by the cambium. Several observers have 

 promulgated or accepted the view that the differences 

 between so-called spring and autumn wood are due to the 

 variations in pressure of the cortex on the cambium, but 

 the view has lately gained ground, based on experimental 

 evidence, that these differences are matters of nutrition, 

 and a recent investigator has declared that the thick- 

 walled elements and small sparse vessels characteristic of 

 autumn wood can be produced, so to speak, at will, by 

 altering the conditions of nutrition. 



It is authoritatively stated that the pines of the cold 

 northern countries are preferred for ships' masts in 

 Europe, and that the wood-cutters and turners of Germany 

 prize especially the timber of firs grown at high elevations 

 in the Bavarian Alps. Now the most striking peculiarity 

 of the timbers referred to is the even quality of the wood 

 throughout : the annual rings are close and show less of 

 the sharp contrasts between thin-walled spring wood and 

 thick-walled autumn wood, and Hartig suggested that this 

 is due to the conditions of their nutrition, and in the 

 following way. The trees at high elevations have their 

 cambium lying dormant for a longer period, and the 

 thickening process does not begin in the lower parts of 

 the trunk until the days are rapidly lengthening and the 

 sun's rays gaining more and more power : the consequence 

 is that the spring is already drawing to a close when the 

 cambium-cells begin to grow and divide, and hence they 

 perform their functions vigorously from the first. 



One of the most interesting experiments in this con- 

 nection came under my observation this summer, owing 

 to the kindness of Prof. Hartig. There is a plantation of 

 larches at Freising near Munich, with young beeches 

 growing under the shade of the larches. The latter are 

 seventy years old, and are excellent trees in every way. 

 About twenty years ago these larches were deteriorating 

 seriously, and were subsequently "under-planted" with 



beech, as foresters say — i.e. beech-plants were introduced 

 under the shade of the larches. The recovery of the 

 latter is remarkable, and dates from the period when the 

 under-planting was made. 



The explanation is based on the observation that the 

 fallen beech-leaves keep the soil covered, and protect it 

 from being warmed too early in the spring by the heat of 

 the sun's rays. This delays the spring growth of the 

 larches : their cambium is not awakened into renewed 

 activity until three weeks or a month later than was 

 previously the case, and hence they are not severely tried 

 by the spring frosts, and the cambium is vigorously and 

 continuously active from the first. 



But this is not all. The timber is much improved : the 

 annual rings contain a smaller proportion of soft, light 

 spring wood, and more of the desirable summer and 

 autumn wood consisting of closely-packed, thick-walled 

 elements. The explanation of this is that the spring 

 growth is delayed until the weather and soil are warmer, 

 and the young leaves in full activity ; whence the cam- 

 bium is better nourished from the first, and forms better 

 tracheides throughout its whole active period. Such a 

 result in itself is sufficient to "repay the investigations 

 of the botanist into the conditions which rule the 

 formation of timber, but this is by no means the only 

 outcome of researches such as those carried on so 

 assiduously by Prof. Hartig in Miinich, and by other 

 vegetable physiologists. 



It is easy to understand that the toughness, elasticity, 

 and such like qualities of a piece of timber, depend on the 

 character of the tracheides, fibres, &c., of which it is chiefly 

 composed. Investigations are showing that the length of 

 such fibres difters in different parts of the tree. Sanio has 

 already demonstrated that in the Scotch pine, for instance, 

 the tracheides differ in length at different heights in the 

 same trunk, becoming longer as we ascend, and also are 

 longer in the outer annual rings than in the inner ones as 

 the tree grows older, up to a certain period ; and this is in 

 accordance with other statements to the general effect 

 that for many years the wood improves, and that better 

 wood is found at the base of the trunk. 



However, it is impossible to pursue these subjects in 

 all their details : my object is served by showing how well 

 worthy of the necessary scientific study is timber even 

 to those who are only concerned with it in its usual con- 

 ditions, and within those limits of variation in structure 

 and function which constitute health. The importance 

 of the subject in connection with the modern develop- 

 ment of biology along the grand road of comparative 

 physiology, does not need insisting upon here. It will 

 be the object of further articles to show how it is, if 

 possible, still more important and interesting to know 

 the structure and functions of healthy timber, before the 

 practical man can understand the diseases to which 

 timber is subject. At the same time it must be clearly 

 borne in mind that these are but sketches of the subject ; 

 for it is as true of trees and their diseases as it is of men 

 and human diseases, if you would be trainers and doctors 

 you must know thoroughly the structures and peculiarities 

 of the beings which are to be under your care. 



H. Marshall Ward. 



{To be continued.) 



NOTES. 



The collections of natural history lately forwarded to the 

 British Museum by Dr. Emin Pasha, from Central Africa, will 

 be described at the meeting of the Zoological Society on 

 January 17. The specimens have been determined by various 

 experts in the different branches of natural history to which 

 they belong. Mr. Oldfield Thomas has prepared a paper on 

 the mammals, amongst which are examples of a remarkable 



