I IO 



NA TURE 



[May 31, 1888 



other details must be passed over, however, and our 

 attention be confined to the fact that here are ample 

 chances for the spores of parasitic and other fungi to 

 fall on a surface admirably suited for their development. 



Fig. 25. — The same piece of stem six years later still: the surface'of the 

 cut branch has now been covered in for some time, and only a boss-like 

 projection marks where the previous cut surface was. This projection is 

 protected by cork layers, like ordinary outer cortex, the old outer cortex 

 cracking more and more as the stem expands. 



The further fact must be insisted upon that numerous 

 fungus-spores do fall and develop upon these wounds, and 

 that by the time the exposed surface is covered in (as in Fig. 

 25) the timber is frequently already rotten, usually for 



Fig. 26. — The same in longitudinal section : lettering as before. Six new 

 layers of wood have been developed, and the cut end of the branch was 

 completely occluded before the last three were formed — i.e. at the end 

 of 1885. After that the cambium became once more continuous round the 

 whole stem, and, beyond a slight protuberance over the occluded wound 

 and the ragged edges of the dead corky outer layers, B, there are r.o 

 signs of a breach. 



some distance down. In the event of fungi, such as have 

 been described above — parasites and wound-parasites — 

 gaining a hold on such wounds, the ravages of the myce- 

 lium will continue after the occlusion is complete, and I 



have seen scores of trees, apparently sound and whole, 

 the interior of which is a mere mass of rottenness : when 

 a heavy gale at length blows them down, such trees are 

 found to be mere hollow shells, the ravages of the 

 mycelium having extended from the point of entry into 

 every part of the older timber. 



In a state of nature the processes above referred to do 

 not go on so smoothly and easily as just described, and it 

 will be profitable to glance at such a case as the following. 



A fairly strong branch dies off, from any cause what- 

 ever— e.g. from being overshadowed by other trees. All 

 its tissues dry up, and its cortex, &c, are rapidly 

 destroyed by saprophytic fungi, and in a short time we 

 find only a hard, dry, branched stick projecting from the 

 tree. At the extreme base, where it joins the tree, the 

 tissues do not at once perish, but for a length of from 

 half an inch to an inch or so the base is still nourished by 

 the trunk. After a time, the wind, or a falling branch, or 

 the weight of accumulated snow, &c, breaks off the dead 

 branch, leaving the projecting basal portion : if the 

 branch broke off quite close to the stem, the wound 



Fig. 27. — Base of a strong branch which had perished naturally twenty-four 

 years previously to the stage figured. The branch decayed, and the 

 base was gradually occluded by the thickening layers of the stem : the 

 fall of the rotting branch did not occur till six years ago, however, 

 as can be determined from the layers at e and/", which then began to- 

 turn inwards over the stump. Meanwhile, the base had become hollow 

 and full of rotten wood, g. It is interesting to note how slight the 

 growth is on the lower side of the branch base, /, as compared with that 

 at h above : the line numbered 24 refers to the annual zones in each case. 

 As seen at b and d, the rotting of the wood passes backwards, and may 

 invade the previously healthy wood for some distance. (After Hartig.) 



would, or at least might, soon be occluded ; but, as it is, 

 the projecting piece not only takes longer to close in, but 

 it tends to rot very badly (Fig. 27), and at the best forms 

 a bad " knot" or hole in the timber when sawn up. Of 

 course what has already been stated of cut branches applies 

 here : the wounds are always sources of danger so long as 

 they are exposed. 



It is beyond the scope of these articles to set forth the 

 pros and cons as to the advisability of adopting any pro- 

 posed treatment on a large scale : the simple question of 

 cost will always have to be decided by those concerned. 

 But whether it is practicable or not on a large scale, 

 there is no question as to the desirability of adopting 

 some such treatment as the following to preserve valuable 

 trees and timber from the ravages of these wound-para- 

 sites. Branches which break off should be cut close 

 down to the stem, if possible in winter, and the clean cut 

 made so that no tearing or crushing of the cambium and 

 cortex occur ; the surface should then be painted with a 

 thorough coating of tar, and the wound left to be occluded. 

 If the cutting is accomplished in spring or summer, 

 trouble will be caused by the tar not sticking to the damp 



