Jan, 19, 1888J 



NATURE 



277 



germinate on the surface of damp timber, and send their 

 germinal filaments into the tracheids, boring through 

 the cell-walls, and extending rapidly in all directions. 

 The fungus mycelium, as it gains in strength by feeding 

 upon the substance of these cell-walls, destroys the wood 

 by a process very similar to that already described (com- 

 pare Fig. 14, Article III.). 



It appears, however, from the investigations of Poleck 

 and Hartig, that certain conditions are absolutely 

 necessary for the development of the mycelium and its 

 spread in the timber, and there can be no question that 

 the intelligent application of the knowledge furnished by 

 the scientific elucidation of the biology of the fungus is 

 the key to successful treatment of the disease. This is, 

 of course, true of all the diseases of timber, so far as they 

 can be dealt with at all, but it comes out so distinctly in 

 the present case that it will be well to examine a little at 

 length some of the chief conclusions. 



Alerulius, like all fungi, consists of relatively large 

 quantities of water — 50 to 60 per cent, of its weight at 

 least — together with much smaller quantities of nitrogen- 

 ous and fatty substances and cellulose, and minute but 

 absolutely essential traces of mineral matters, the chief of 

 which are potassium and phosphorus. It is not necessary 

 to dwell at length on the exact quantities of these matters 

 found by analysis, nor to mention a few other bodies of 

 which traces exist in such fungi. The point just now is 

 that all these materials are formed by the fungus at the 

 expense of the substance of the wood, and for a long time 

 there was considerable difficulty in understanding how 

 this could come about. 



The first difficulty was that although the " dry-rot 

 fungus" could always be found, and the mycelium was 

 easily transferred from a piece of diseased wood to a" 

 piece of healthy wood provided they were in a suitable 

 warm, damp, still atmosphere, no one had as yet suc- 

 ceeded in causing the spores of the Meruliiis to germinate, 

 or in following the earliest stages of the disease. Up 

 to about the end of the year 1884 it was known that the 

 spores refused to germinate either in water or in decoc- 

 tions of fruit; and repeated trials were made, but in vain, 

 to see them actually germinate on damp wood, until two 

 observers, Poleck and Hartig, discovered about the 

 same time the necessary conditions for germination. 

 It should be noted here that this difficulty in persuading 

 spores to germinate is by no means an isolated instance: 

 we are still ignorant of the conditions necessary for the 

 germination of the spores of many fungi— ^.^. the spores of 

 the mushroom, according to De Bary ; and it is known 

 that in numerous cases spores need very peculiar treat- 

 ment before they will germinate. The peculiarity in the 

 case of the spores of Mcrulius lacrymans was found by 

 Hartig to be the necessity of the presence of an alkali, 

 such as ammonia ; and it is found that in cellars, stables, 

 and other outhouses where ammoniacal or alkaline 

 emanations from the soil or elsewhere can reach the 

 timber, there is a particularly favourable circumstance 

 afforded for the germination of the spores. The other 

 conditions are provided by a warm, still, damp atmosphere, 

 such as exists in badly ventilated cellars, and corners, and 

 beneath the flooring of many buildings. 



Careful experiments have shown beyond all question 

 that the " dry-rot fungus " is no exception to other fungi 

 with respect to moisture : thoroughly dry timber, so long 

 as it is kept thoroughly dry, is proof against the' disease 

 we are considering. Nay, more, the fungus is peculiarly 

 susceptible to drought, and the mycelial threads and even 

 the young fructifications growing on the surface of abeam 

 of timber in a damp close situation may be readily killed 

 in a day or two by letting in thoroughly dry air : of 

 course, the mycelium deeper down in the wood is not so 

 easily and quickly destroyed, since not only is it more 

 protected, but the mycelial strands are able to transport 

 moisture from a distance. Much misunderstanding pre- 



vails as to the meaning of "dry air " and "dry wood": 

 as a matter of fact, the air usually contains much 

 moisture, especially in cellars and quiet corners devoid of 

 draughts, such as Merulius delights in, and we have 

 already seen how dry timber rapidly absorbs moisture 

 from such air. Moreover, the strands of mycelium may 

 extend into damp soil, foundations, brick-work, &c. ; in, 

 such cases they convey moisture to parts growing in 

 apparently drj' situations. 



A large series of comparative experiments, made 

 especially by Hartig, have fully established the correct- 

 ness of the conclusion that damp foundations, walls, 

 &c., encourage the spread of dry-rot, quite inde- 

 pendently of the quality of the timber. This is im- 

 portant, because it has long been supposed that timber 

 felled in summer was more prone to dry-rot than timber 

 felled in winter : such, however, is not shown to be the 

 case, for under the same conditions both summer- and 

 winter-wood suffer alike, and decrease in weight to the 

 same extent during the progress of the disease. There 

 is an excellent opportunity for further research here 

 however, since one observer maintains that in one case at 

 any rate {Pinus sylvestris) the timber felled at the end of 

 April suffered from the disease, whereas that felled in 

 winter resisted the attacks of the fungus : internal evi- 

 dence in the published account supports the suspicion 

 that some error occurred here. The wood which suc- 

 cumbed was found to contain much larger quantities of 

 potassium and phosphorus (two important ingredients for 

 the fungus), and Poleck suggests that this difference Jn 

 chemical constitution explains the ease with which his 

 April specimens were infected. ; ■ : 



It appears probable from later researches and criticism 

 that Poleck did not choose the same parts of the two 

 stems selected for his experiments, for (in the case of 

 Pin us sylvestris) the heart-wood is attacked much less 

 energetically than the sap-wood — a circumstance which 

 certainly may explain the questionable results if the 

 chemist paid no attention to it, but analyzed. the sap-wood 

 of one and the heart-wood of the other piece of timber, 

 as he seems to have done. 



The best knowledge to hand seems to be that no 

 difference is observable in the susceptibility to dry-rot of 

 winter-wood and summer-wood of the same timber ; i.e. 

 Merulius lacrymans will attack both equally, if other 

 conditions are the same. 



But air-dry and thoroughly seasoned timber is much 

 less easily attacked than damp fresh-cut wood of the 

 same kind, both being exposed to the same conditions. 



Moreover, different timbers are attacked and destroyed 

 in different degrees. The heart-wood of the pine is more 

 resistant than any spruce timber. Experimental obser- 

 vations are wanted on the comparative resistance of oak> 

 beech, and other timbers, and indeed the whole question 

 is well worth further investigation. 



When the spore has germinated, and the fungus hyphas 

 have begun to grow and branch in the moist timber, they 

 proceed at once to destroy and feed upon the contents of 

 the medullary rays ; the cells composing these contain 

 starch and saccharine matters, nitrogenous substances, 

 and inorganic elements, such as potassium, phosphorus, 

 calcium, &c. Unless there is any very new and young 

 wood present, this is the only considerable source of 

 proteid substances that the fungus has : no doubt a little 

 may be obtained from the resin-passages, but only the 

 younger ones. In accordance with this a curious fact 

 was discovered by Hartig : the older parts of the hyphas 

 -pass their protoplasmic contents on to the younger growing 

 portions, and so economize the nitrogenous substances. 

 Other food-substances are not so sparse ; the lignified 

 walls inclose water and air, and contain mineral salts, and 

 such organic substances as coniferin, tannin, &c., and 

 some of these are absorbed and employed by the fungus. 

 Coniferin especially appears to be destroyed by the hyphae. 



