276 



NATURE 



{yait. 19, I 



The usual signs of the ordinary dry-rot of timber in 

 buildings, especially deal-timber or fir- wood, are as follows. 

 The wood becomes darker in colour, dull yellowish-brown 

 instead of the paler tint of sound deal ; its specific weight 

 diminishes greatly, and that this is due to a loss of sub- 

 stance can be easily proved directly. These changes are 

 accompanied with a cracking and warping of the wood, 

 due to the shortening of the elements as water evaporates 

 and they part from one another : if the disease affects one 

 side of a beam or plank, these changes cause a pro- 

 nounced warping or bending of the timber, and in bad 

 cases it looks as if it had been burnt or scorched on the 

 injured side. If the beam or plank is wet, the diseased 

 parts are found to be so soft that they can easily be cut 

 with a knife, almost like cheese ; when dry, however, the 

 touch of a hard instrument breaks it into brittle fibrous 

 bits, easily crushed between the fingers to a yellow-brown, 

 snuff-like powder. The timber has by this time lost its 

 coherence, which, as we have seen, depends on the firm 

 interlocking and holding together of the uninjured fibrous 

 elements, and may give way under even light loads — a 

 fact only too well known to builders and tenants. The 

 walls of the wood-elements (tracheides, vessels, fibres, 



be extending themselves on to neighbouring pieces of 

 timber, or even on the brick-work or ground on which the 

 timber is resting. These cord-like strands and cake-like 

 masses of felt, with their innumerable fine filamentous 

 continuations in the wood, constitute the vegetative body 

 or mycelium of a fungus known as Mernlins lacrymans. 

 Under certain circumstances, often realized in cellars and 

 houses, the cakes of mycelium are observed to develop 

 the fructification of the fungus, illustrated in Fig. 18. 



To understand the structure of this fructification we 

 may contrast it with that of the Polyporus or Travietcs 

 referred to in the last article ; where in the latter we find 

 a number of pores leading each into a tubular cavity lined 

 with the cells which produce the spores, the Meruliiis 

 shows a number of shallow depressions lined by the 

 sporogenous cells. The ridges which separate these de- 

 pressed areolae have a more or less zigzag course, running 

 together, and sometimes the whole presents a likeness to 



Fig. 17. — Portion of the niyceliu.u oi Meriilius laciymans removed fro ii 

 the surface of a beam of wood. This cake-like mass spreads over the 

 surface of the timber, to which it is intimately attached by hyphae run- 

 ning in the wood-substance. Subsequently it develops the spore-bearing 

 areolae near its edges. The shading indicates differences in colour, as 

 well as irregularities of surface. 



or cells, according to the kind of timber, and the part 

 affected) are now, in fact, reduced more or less to 

 powder, and if such badly diseased timber is placed in 

 water it rapidly absorbs it and sinks : the wood in this 

 condition also readily condenses and absorbs moisture 

 from damp air, a fact which we shall see has an important 

 bearing on the progress of the disease itself. 



If such a piece of badly diseased deal as I have shortly 

 described is carefully examined, the observer is easily 

 convinced that fungus filaments (mycelium) are present 

 in the timber, and the microscope shows that the finer 

 filaments of the mycelium (hyphse) are permeating the 

 rotting timber in all directions — running between and in 

 the wood elements, and also on the surface, much 

 as in the case shown in Fig. 17. In a vast number 

 of cases, longer or shorter, broader or narrower, cords 

 of grayish-white mycelium may be seen coursing on the 

 surface and in the cracks : in course of time there will 

 be observed flat cake-like masses of this mycelium, the 

 hyphas being woven into felt-like sheets, and these may 



Fig. 18.— Mature frnciification of McriiUns lacryjnans. The cake-hke 

 mass of felted mycelium has developed a series of areolae (in the upper 

 part of the figure), on the walls of which the spores are produced. In 

 the natural position this spore-bearing layer is turned downward ■;, and 

 in a moist environment pellucid drops or " tears " distil from it. The 

 barren part in the foreground was on a wall, and the remainder on the 

 lower side of a beam : the fungus was photographed in this position to 

 show the structure. 



honey-comb ; if the ridges were higher, and regularly 

 walled in the depressed areas, the structure would corre- 

 spond to that of a Polyporus in essential points. The 

 spores are produced in enormous numbers on this areolated 

 surface, which is directed downwards, and is usually 

 golden-brown, but may be dull in colour, and presents 

 the remarkable phenomenon of exuding drops of clear 

 water, like tears, whence the name lacrymatis. In well- 

 grown specimens, such as may sometimes be observed 

 on the roof of a cellar, these crystal-like tears hang 

 from the areolated surface like pendants, and give an 

 extraordinarily beautiful appearance to the whole ; the 

 substance of the glistening Mcridiiis may then be like 

 shot-velvet gleaming with bright tints of yellow, orange, 

 and even purple. 



It has now been demonstrated by actual experiment 

 that the spores of the fungus, Aferulius lacryma/is, will 



