Jan. 12, 1888J 



NATURE 



25, 



consistency ; bright yellow below, where the numerous 

 minute pores are, and orange or somewhat vermilion 

 above, giving the substance a coral-like appearance. I 

 have often seen it in the neighbourhood of Englefield 

 Green and Windsor, and it is very common in England 

 generally. 



If the spore of this Polyporus lodges on a wound which 

 exposes the cambium and young wood, the filaments 

 grow into the medullary rays and the vessels, and soon 

 spread in all directions in the timber, especially longi- 

 tudinally, causing the latter to assume a warm brown 

 colour and to undergo decay. In the infested timber are 

 to be observed radial and other crevices filled with the 

 dense felt-like mycelium formed by the common growth 

 of the innumerable branched filaments. In bad cases it 

 is possible to strip sheets of this yellowish white felt-work 

 out of the cracks, and on looking at the timber more 

 closely (of the oak, for instance) the vessels are found to 

 be filled with the fungus filaments, and look like long 

 white streaks in longitudinal sections of the wood — 

 showing as white dots in transverse sections. 



It is not necessary to dwell on the details of the 

 histology of the diseased timber : the ultimate filaments 

 of the fungus penetrate the walls of all the cells and 

 vessels, dissolve and destroy the starch in the medullary 

 rays, and convert the lignified walls of the wood elements 

 back again into cellulose. This evidently occurs by some 

 solvent action, and is due to a ferment excreted from the 

 fungus filaments, and the destroyed timber becomes 

 reduced to a brown mass of powder. 



1 cannot leave this subject without referring to a remark- 

 ably interesting museum specimen which Prof. Hartig 

 showed and explained to me this summer. This is a block 

 of wood containing an enormous irregularly spheroidal 

 mass of the white felted mycelium of this fungus, Polyporus 

 sulphureus. The mass had been cut clean acros^s, and 

 the section exposed a number of thin brown ovoid bodies 

 embedded in the closely-woven felt: these bodies were of 

 the size and shape of acorns, but were simply hollow 

 shells filled with the same felt-like mycelium as that in 

 which they were embedded. They were cut in all direc- 

 tions, and so appeared as circles in some cases. These 

 bodies are, in fact, the outer shells of so many acorns, 

 embedded in and hollowed out by the mycelium of 

 Polyporus sulphureus. Hartig's ingenious explanation 

 of their presence speaks for itself. A squirrel had stored 

 up the acorns in a hollow in the timber, and had not 

 returned to them — what tragedy intervenes must be left 

 to the imagination. The Polyporus hid then invaded the 

 hollow, and the acorns, and had dissolved and destroyed 

 the cellular and starchy contents of the latter, leaving 

 only the cuticularized and corky, shells, looking exactly 

 like fossil eggs in the matrix. I hardly think geology 

 can beat this for a true story. 



The three diseases so far described serve very well as 

 types of a number of others known to be due to the 

 invasion of timber and the dissolution of the walls of its 

 cells, fibres, and vessels by Hymenomycetous fungi, i.e. 

 by fungi allied to the toadstools'and polypores. They all 

 " rot " the timber by destroying its structure and sub- 

 stance, starting from the cambium and medullary rays. 



To mention one or two additional forms, Trametes 

 Pint is common on pines, but, unlike its truly parasitic 

 ally, Jr. nidiciperda, which attacks sound roots, it is a 

 vyound-parasite, and seems able to gain access to the 

 timber only if the spores germinate on exposed surfaces. 

 The disease it produces is very like that caused by its 

 ally : probably none but an expert could distinguish 

 between them, though the differences are clear when the 

 histology is understood. 



Polyporus fulvus is remarkable because its hyphse 

 destroy the middle-lamella, and thus isolate the tracheides 

 in the timber of firs ; Polyporus borealis also produces 

 disease in the timber of standing Conifer^ ; Polyporus 



igniarius is one of the commonest parasites on trees such 

 as the oak, &c.,and produces in them a disease not unlike 

 that due to the last form mentioned ; Polyporus dryadcus 

 also destroys oaks, and is again remarkable because its 

 hyphaj destroy the middle-lamella. 



With refereace to the two fungi last mentioned I can- 

 not avoid describing a specimen in the Museum of Forest 

 Botany in Miinich, since it seems to have a possible 

 bearing on a very important question of biology, viz. the 

 action of soluble ferments. 



It has already been stated that soma of these tree- 

 killing fungi excrete ferments which attack and dissolve 

 starch-grains, and it is well known that starch-grains are 

 stored up in the cells of thi medullary rays found in 

 timber. Now, Polyporus dryadcus and P. igniarius are 

 such fungi ; their hyph^ excrete a ferment which com- 

 pletely destroys the starch-grains in the cells of the 

 medullary rays of the oak, a tree very apt to be attacked 

 by these two parasites, though P. igniarius, at any rate, 

 attacks many other dicotyledonous trees as well. It 

 occasionally happens that an oak is attacked by both of 

 these Polyporei, and their mycelia become intermingled 

 in the timber : when this is the case the starch-grains 

 remain intact in thosi cells which are invaded simul- 

 taneously by the hyphcc of both fungi. Prof. Hartig 

 lately showed me longitudinal radial sections of oak- 

 timber thus attacked, and the medullary rays showed up 

 as glistening white plates. These plates consist of nearly 

 pure starch : the hyphae have destroyed the cell-walls, but 

 left the starch intact. It is easy to suggest that the two 

 ferments acting together exert (with respect to the starch), 

 a sort of inhibitory action one on the other ; but it is also 

 obvious that this is not the ultimate explanation, and one 

 feels that the matter deserves investigation. 



It now becomes a question— What other types of timber- 

 diseases shall be described? Of course the limits of a 

 popular article are too narrow for anything approaching 

 an exhaustive treatment of such a subject, and nothing 

 has as yet been said of several other diseases due to 

 crust- like fungi often found on decaying stems, or of others 

 due to certain minute fungi which attack healthy roots. 

 Then there is a class of diseases which commence in the 

 bark or cortex of trees, and extend thence into the 

 cambium and timber : some of these " cankers," as they are 

 often called, are proved to be due to the ravages of fungi, 

 though there is another series of apparently similar 

 "cankers" which are caused by variations in the environ- 

 ment — the atmosphere and weather generally. 



It would need a long article to place the reader au 

 courant with the chief results of what is known of these 

 diseases, and I must be content here with the bare state- 

 ment that these " cankers " are in the main due to local 

 injury or deUruction of the cambium. If the normal 

 cylindrical sheet of cambium is locally irritated or de- 

 stroyed, no one can wonder that the thickening layers of 

 wood are not continued normally at the locality in ques- 

 tion : the uninjured cells are also influenced, and abnormal 

 cushions of tissue formed which vary in different cases. 

 Now, in "cankers" this is — put shortly — what happens: 

 it may be, and often is, due to the local action of a para- 

 sitic fungus ; or it may h^ — and, again, often is— owing 

 to injuries produced by the weather, in the broad sense, 

 and saprophytic organisms may subsequently invade the 

 wounds. 



The details as to how the injury thus set up is propa- 

 gated to other parts— how the " canker " spreads into the 

 bark and wood around— a/v details, and would require 

 considerable space for their description : the chief point 

 here is again the destructive action of mycelia of various 

 fungi, which by means of their powers of pervading the 

 cells and vessels of the wood, and of secreting soluble 

 ferments which break down the structure of the timber, 

 render the latter diseased and unfit for use. The only 

 too well known larch-disease is a case in point ; but, since 



