Jan. 5, 1888] 



NA TURE 



229 



from one of the diseased roots or stems, there may be 

 seen the flat, silky, white bands of mycelium running in 

 the plane of the cambium, and here and there protruding 

 tiny white cushions between the scales of the bark (Fig. 

 12) ; in advanced stages the fructifications developed 

 from these cushions may also be found. The wood inside 

 the diseased root will be soft and damp, and in a more or 

 less advanced stage of decomposition. 



On examining the timber itself, we again obtain dis- 

 tinctive characters which enable the expert to detect the 

 disease at a glance. I had the good fortune to spend 

 several pleasant hours in the Munich Museum examining 

 and comparing the various diseases of timbers, and it is 

 astonishing how well marked the symptoms are. In the 

 present case the wood at a certain stage presents the 

 appearance represented in the drawing, Fig. 13. The 

 general tone is yellow, passing into a browner hue. 

 Scattered here and there in this ground-work of still 

 sounder wood are peculiar oval or irregular patches of 

 snowy white, and in the centre of each white patch is a 

 black speck. Nothing surprised me more than the accu- 



FiG. 13. — A block of the timber of a spruce-fir, attacked by Trainetes 

 radiciperda. The general colour is yellow, and in the yellow matrix 

 of less rotten wood are soft white patches, each with a black speck in 

 it. These patches are portions completely disorganized by the action 

 of the mycelium, and the appearance is very characteristic of this 

 particular disease. (After Hartig.) 



racy with which Prof. Hartig's figures reproduce the 

 characteristic appearance of the original specimens in 

 his classical collection, and I have tried to copy this in 

 the woodcut, but of course the want of colour makes 

 itself evident. 



It is interesting and important to trace the earlier 

 changes in the diseased timber. When the filaments of 

 the fungus first begin to enter the wood, they grow upwards 

 more rapidly than across the grain, piercing the walls of 

 the cells and tracheides by means of a secretion — a soluble 

 ferment — which they exude. This ferment softens and 

 dissolves the substance of the walls, and therefore, of 

 course, destroys the structure and firmness, &c., of the 

 timber. Supposing the filaments to enter cells which 

 still contain protoplasm and starch, and other nutritive 

 substances (such as occur in the medullary rays, for ex- 

 ample), the filaments kill the living contents and feed on 

 them. The result is that . what remains unconsumed 

 acquires a darker colour, and this makes itself visible in 

 the mass to the unaided eye as a rosy or purple hue, 

 gradually spreading through the attacked timber, As the 



destructive action of the fungus proceeds in the wood, the 

 purple shades are gradually replaced by a yellowish cast, 

 and a series of minute black dots make their appearance 

 here and there ; then the black dots gradually surround 

 themselves with the white areas, and we have the stage 

 shown in Fig. 13. 



These white areas are the remains of the elements of 

 the wood which have already been completely delignified 

 by the action of the ferment secreted by the fungus fila- 

 ments — i.e. the hard woody cell-walls have become con- 

 verted into soft and swelling cellulose, and the filaments 

 are dissolving and feeding upon the latter (Fig. 14). In 

 the next stage of the advancing destruction of the timber 

 the black dots mostly disappear, and the white areas get 

 larger ; then the middle-lamella between the contiguous 



Fig. 14. — Sectional view of a tracheide of the spruce-fir, attacked by the 

 hyphae (a, h) of a Trametes, highly magnified (after Hartig). The 

 upper part of the tracheide has its walls still sound, though already 

 pierced by the hyphae ; the lower part (c) has the walls completely 

 delignified, and converted into cellulose, which swells up and dissolves 

 The middle-lamella is also undergoing diss lution. The holes in the 

 walls have been bored by hyph e. 



elements of the wood becomes dissolved, and soft places 

 and cavities are produced, causing the previously firm 

 timber to become spongy and soft, and it eventually breaks 

 up into a rotting mass of vegetable remains. 



It will readily be understood that all these progressive 

 changes are accompanied by a decrease in the specific 

 gravity of the timber, for the fungus decomposes the sub- 

 stance much in the same way as it is decomposed by 

 putrefaction or combustion, i.e. it causes the burning off 

 of the carbon, hydrogen, and nitrogen, in the presence of 

 oxygen, to carbon-dioxide, water, and ammonia, retaining 

 part in its own substance for the time being, and Hving at 

 its expense. H. .Marshall Ward 



{To be continued.) 



PROFESSOR ALEXANDER DICKSON. 



THE close of 1887 has been marked by a long death- 

 roll in the ranks of science. In the company of 

 botanists it has been especially heavy, and now the sad 

 news of the tragically sudden death of Prof. Alexander 



