130 



KNOWLEDGE. 



May, 1915. 



from the spores travelled along the surface of the 

 mica until they came to one of the tiny holes, 

 down which they passed into the nutritive substance 

 below it. The spores of most fungi germinate 

 best directly they are shed, as they are in most 

 cases frail bodies, easily destroyed by adverse 

 conditions. Fischer showed that the spores of the 

 Beechtuft germinated slowly and with difficulty 

 after a month, and after six weeks failed to ger- 

 minate at all. Unlike most plants, the fungus plant, 

 or mycelium, is capable of withstanding adverse 

 conditions much better than are its spores. The 

 mycelium is really the resting stage. 



Toadstools often come up in nearly the same spot 

 year after year. In a garden near the centre of 

 London the Horse Mushroom (Psalliota arvensis) 

 (see Figure 103) has appeared every year for the 

 last fourteen years to my certain knowledge. 

 There is an oak tree in Epping Forest on which 

 the Beefsteak Fungus (Fistulina hepaiica) has 

 been seen by me almost every year for 

 the last ten years. Fries mentions that he 

 had found a somewhat rare toadstool growing from 

 a beech tree in 1815, and that he again found the 

 same fungus appearing from the same crack in 

 the same tree in 1833, but had seen nothing of it in 

 the intervening years. The vulnerability of the 

 spores is so great that some fungi have given up 

 the production of spores completely, and are 

 reproduced entirely by the separation of pieces of 

 their mycelium. A good example of this in the 

 case of ryegrass will be described later. Smut 

 is a disease which affects many of the cereal plants. 

 Its minute spores are sown with the seeds, and 

 directly the seeds germinate the fungus infects the 

 tiny plants. By washing the oats with a disinfectant 

 before they are sown the fungus is killed and smut 

 is prevented. But in the case of barley the treat- 

 ment is found to be of no value, because the smut 

 fungus enters the ovary of the barley while it is in 

 the flower stage, and thus passes into the seed. 

 In this condition it remains dormant until the seed 

 is sown, when it again awakens into activity. 

 It is probable that the mycelium of most fungi 

 can go on existing for man}' years in the soil without 

 producing fruit bodies or toadstools. Thus we find 

 that some years mushrooms are very plentiful and in 

 others very scarce. After a warm, wet summer, 

 fields and meadows abound with toadstools which 

 are hardly to be seen at all under more normal 

 circumstances. It is probable in these cases that 

 the mycelium has existed for many years in the 

 soil, but that only after the warm, moist weather 

 has it obtained sufficient vitality to determine on 

 the production of spores by means of toadstools. 

 There is also a certain amount of evidence to show 

 that some kinds of toadstools are found in abund- 

 ance in some localities every third year. It is clear, 

 then, that the mycelium, and not the spore, is the 

 true resting stage in the case of many fungi. 



In some forms of fungus the mycelium forms 



itself into a firm, dense mass before passing into the 

 resting stage : these masses are called " sclerotia." 

 Hard black bodies are not infrequently seen in the 

 interior of the dead stems of the potato, cucumber, 

 and man}' other plants. These remain dormant 

 for a time, and later on the fructification of the 

 fungus, shaped like a cup in many cases and con- 

 nected to the sclerotium by fine threads, appears. 

 The pretty little toadstool shown in Figure 99 is 

 usually found growing on the dead " fruit " of another 

 of its kind. From the mycelium small sclerotia are 

 produced, and from these the tiny toadstools 

 spring up. Ergot is another example of a sclero- 

 tium. Large elongated bodies are seen, which form 

 the resting stage of the fungus. They fall to the 

 ground in autumn, and remain there dormant all 

 the winter. From these black bodies short stalks 

 with purple heads arise in spring, and from these 

 the spores are given off. In some fungi the resting 

 mycelium takes the form, not of sclerotia, but of 

 strands and threads : these are spoken of as 

 " rhizomorphs." Dark, hair-like threads are often 

 found among dead leaves : they are rhizomorphs 

 of a species of Marasmiiis. Underneath the bark 

 of many a dying tree dark interlacing cords may 

 be observed which are the rhizomorphs of the Stump- 

 tuft (Armillaria mcllca) (see Figures 101 and 1 04), 

 one of the most destructive of parasitic fungi, 

 and the cause of one of the most serious forms of 

 timber disease. The fruits of the Stumptuft are 

 generally found near the bases of trees. A 

 large mass of them appears in Figure 101. The 

 fungus reaches the trees in many cases through 

 a wound, and the mycelium from the germinating 

 spore spreads in the cambium, that is, the growing 

 tissue between the bark and the wood, and forms 

 its rhizomorphs in this region. As it extends inward 

 the wood is destroyed and the tree is slowly killed, 

 and from the root of the infected tree rhizomorphs 

 extend through the soil to infect other trees. 

 From these rhizomorphs the fruit or toadstool 

 may be formed, so that Stumptufts may be found 

 some little distance from the tree on which their 

 mycelium is growing (see Figure 101). It is an 

 interesting fact that rhizomorphs which carry in- 

 fection from tree to tree are hardly ever found more 

 than six or eight inches from the surface of the soil. 

 A trench at least a foot deep round an infected tree 

 will prevent the spread of the disease by the means 

 of rhizomorphs to other trees around. 



That many toadstools tend to come up in rings 

 has been noticed for a very long time, and many 

 fantastic suggestions have been invented to explain 

 the fact, several examples of which may be seen in 

 Figures 105, 106, 108, and 110. The best known 

 of these is perhaps the Fairy-ring Toadstool 

 {Marasmius oreades), but gigantic rings of the Giant 

 Puffball (Lycoperdon gigantciini) arc also often seen 

 on limestone downs, and it is curious that in most 

 cases when no toadstools are to be found the rings 

 are still recognisable through the darker colour 



