134 



KNOWLEDGE. 



May, 1915. 



one species of plant. Indeed, in some of the smaller 

 parasites, specialisation has gone so far that a given 

 fungus will only grow on a single variety of host 

 plant. 



The ecology ot fungi, or their relationship to 

 the environment in which they grow, is a subject 

 about which little is known. Toadstools >eem less 

 influenced by the mineral character of the soil 

 than by the other plants which are growing with 

 them. The Morel {Morchella esculenta) (see 

 Figure I Id) is, however, to some extent confined to 

 limestone districts. Every variety of wood has its 

 definite fungus flora, which is fairly constant from 

 year to year. The toadstools met with in a pinewood 

 are very different from those found in an ordinary 

 mixed wood, but in both wc find the same species 

 coming up at approximately the same spot year 

 after year. Should, however, any change in the 

 character of the wood take place, such as the cutting 

 down of a number of the trees or extensive removal 

 of the undergrowth, a great change in the fungus 

 flora is at once to be noticed. Generally it may be 

 said that the presence of thick brushwood seems to 

 interfere with the development and growth of 

 fungi. The constant association of certain toad- 

 stools and certain trees, as, for instance, the Fly 

 Agaric {Amanita uiuscaria) (see Figure 119), which 

 is almost exclusively found near birch trees, sug- 

 gests that there may be some symbiotic relation- 

 ship between the two plants by which one is of 

 some assistance to the other. Massee is of opinion 

 that the mycelium of black -spored toadstools is 

 destroyed by that of toadstools with lighter-coloured 

 spores, or that, at any rate, its growth is much 

 interfered with. But I have seen a variety of 

 Coprinus with black spores growing apparently 

 happily on the same log with white-spored species. 

 Sometimes four or five different varieties of toad- 

 stool are seen on the same decaying tree, and one 

 would very much like to know how the mycelium 

 of each is behaving with regard to that of the 

 others. Two species of Poly poms (P. ignatarius and 

 P. dryadcus) both grow on the oak parasitically. 

 When growing alone, each absorbs the starch 

 contained in the medullary rays, as well as the 

 lignin of the wood ; but when the oak is infected 

 by both together, the starch of the medullary rays 

 remains intact, although the lignin is absorbed. 

 Why this is nobody knows. 



Fungi are not infrequently to be found in most 

 unexpected places, and some seem almost invari- 

 ably associated with human habitations. When 

 a waterpipe bursts inside a house, or the rain comes 

 in through the roof, a wet place is seen on the wall 

 or ceiling. If the leak is not attended to, and the 

 area remains damp for several days, a pink or 

 pale brown discoloration soon becomes visible, 

 especially if the affected area is whitewashed or 

 plastered. If the discoloration is examined care- 

 fully, and especially if a pocket lens is used, it will 

 be noticed that the colour is due to a number of 



minute raised spots, all of about the same size. 

 These spots are the fructifications of a tiny fungus 

 (Pcziza domestica) which appears to grow exclu- 

 sively on a moist whitewashed surface. Another 

 fungus, which we sometimes meet with to our cost, 

 is the Dry-rot Fungus [Merulius lacrymans) (see 

 Figure 1 17). The " lacrymans " part of the name 

 refers, not to the tears of the householder — appro- 

 priate as they may be — but rather to the large clear 

 drops of moisture which are exuded from the fruit 

 of the fungus. Often the first indication that we 

 have of the presence of the dry-rot fungus is the 

 repeated appearance of a fine brown dust which 

 comes into the room through a crack in the floor 

 or wainscot, and is in reality some of the spores 

 given off from the fructification. A little later on 

 the woodwork may appear moist, or, if covered by 

 paint, a certain amount of warping may be noticed, 

 or even at times the first thing that may be observed 

 is that the floor gives way, and somebody's foot 

 nearly goes through. The fungus grows best in 

 dark, moist, unventilated places ; but even where 

 such areas are dry the plant, spreading from 

 moist soil or brickwork, may carry sufficient 

 moisture with it to destroy the timber or woodwork 

 which it invades. Wood that is infected by the 

 fungus is either moist, soft, and reddish brown in 

 colour, or else dry, brown, and powdery, and much 

 lighter in weight than ordinary wood ; and in any 

 case, whether wet or dry, it is much more brittle 

 than healthy timber. The mycelium of the fungus 

 is white and silky : it may sometimes be seen 

 spreading over the surface of boxes or woodwork 

 in dark cellars. Apart from the dwellings of man 

 the fungus is rarely seen, but I have once met with 

 its fruit growing on a forest tree. For a long time 

 all attempts to induce the spores of the dry-rot 

 fungus to germinate experimentally proved un- 

 successful, but when the nutritive medium was 

 made faintly alkaline by the addition of ammonia, 

 the spores grew readily ; and it is probable that 

 ammonia is very often present in minute quantities 

 in the atmosphere of the dark, unventilated spots 

 where the fungus has its home. 



A group of fungi which I found growing from a 

 roof of a London cellar is seen in Figure 121. 

 These were hanging downwards, and the attempt 

 made by the plant to get its gills into the vertical 

 plane, so that its spores may be satisfactorily 

 shed, is clearly seen in the photograph. Clitocybe 

 tabescens is not exclusively found in connection with 

 mankind. It grows also in the forest on decaying 

 wood. 



There would seem to be no very hard-and-fast 

 line of division between fungi which live exclusively 

 on dead material and those which are capable of 

 attacking living animals and plants. Not a few 

 seem to be able to grow equally successfully as 

 saprophytes and parasites. A good many parasitic 

 fungi are in nature confined to a single species of 

 plant, but it has been found possible in some cases 



