AN EXPLOSIVE FUNGUS. 



By P. J. ALEXANDER. 



Among the various kinds of British fungi none, to 

 my mind, are more interesting than those which, 

 when mature, explode like a gun, shooting their 

 spores several feet into the air. Some of these 

 " ball-throwing " fungi belong to the Mucoraceae, a 

 family of the true moulds (Phycomycetae). 



The easiest type of this class to find, and the one 

 that presents the greatest facilities for study (as 

 most of its movements can be watched with the 

 naked eye), is Pilobolus crystallinus. It may be 

 found in spring, summer, and autumn growing in 

 close clusters on all mammal dung, and especially 

 on that of horses, cows, pigs, and sheep. I have like- 

 wise met with it on the droppings of birds. It first 

 came to my notice quite by accident. One day, in 

 my country rambles, I observed some small red 

 pezizas on the sweepings from a sheep pen, and I 

 took some home with me in a tin box that I always 

 carry with me on such occasions. The next 

 morning on going to examine my find I was 

 astounded and delighted to see dense numbers of 

 crystalline bulbs surmounted by a black cap and 

 interspersed with tubes of a beautiful golden colour. 

 I kept the medium on which they were growing 

 moist, and examined the development of this new 

 fungus for ten consecutive days, and I think the 

 results of my observations and study may prove 

 interesting to readers of " Knowledge." 



History. — This fungus was apparently unknown a 

 hundred and fifty years ago — at least we find no 

 mention of it in any literature prior to that date. 

 Scopoli was the first to call attention to it under 

 the synonym of Mucor obliquus in 1772 ; but it was 

 Wiggers who first enabled botanists to recognise 

 this fungus by his description of it published in 

 1780. It is a curious fact that Tode, whose name is 

 usually connected with this species, did not study it 

 till four years later. We come across it, it is true, 

 in a French work by Leveille and Durieu de 

 Maisonneuve in 1826; but they did little to 

 elucidate a knowledge of this fungus, as many 

 of their observations were erroneous. F. Cohn 

 noticed it in 1851, and Francis Currey further 

 investigated its formation in 1857. Two years 

 later a Belgian botanist and a native of Louvain 

 published his famous monograph on the subject, 

 showing that he had made a complete analysis 

 of this particular fungus, though still leaving one 

 or two questions unsolved. 



Growth. — The first sign of this fungus on the 

 surface of the dung is a tiny golden speck, which, 

 however, soon becomes elongated and shoots up in a 

 golden finger-like tube. About three hours later 

 this tube swells out at the top into a small globe 

 (see Figure 532 a, b, c). Soon after this it loses its 

 colour, the tube and bulb become crystalline, and a 

 black hemispherical cap is formed on the top of the 

 bulb. This cap is the sporangium containing the 



spores or reproductive bodies. At first it does not 

 seem very distinct from the rest of the bulb (see 

 Figure 532 e), but little by little a clear line of 

 demarcation becomes visible (see Figure 532 /). 

 The Pilobolus is now reaching maturity and ready 

 to discharge its spores. It is filled with a trans- 

 parent liquid which is slightly acid. Beads of 

 moisture often form along the stem and hang like 

 pearls around the bulb, giving the fully developed 

 fungus a most beautiful and delicate appearance (see 

 Figure 532 /). We can even observe with an 

 ordinary lens small worm-like animalcules moving 

 in the swollen bulb. It is now time to collect the 

 spore. The best way to do this is to hold a piece of 

 white paper a few inches over the black capsules. 

 If the light is good the tension soon becomes too 

 great and the caps are blown off with great force. 

 They are sometimes thrown to a height of three 

 feet. Before alighting on the paper they turn a 

 somersault in the air, so as not to strike the surface 

 with their convex side, but fall on the paper like an 

 inverted cup, shutting up the spores inside. This 

 black cap is made of a remarkably tough membrane 

 as we soon discovered in making a microscopic 

 preparation of the same (see Figure 534 g, which shows 

 this sporangium, about six hundred times enlarged, full 

 of yellow spores, ellipsoidal in shape). If the fungus 

 is not allowed sufficient light, or if the atmosphere 

 be too warm, instead of projecting the sporangium, 

 the whole fungus withers and topples over (see 

 Figure 533), and soon nothing is seen but a whitish 

 powder left by the dried-up skin of the stem. 



The whole plant grows, develops, and dies within 

 twenty-four hours. If left out in the open in its 

 natural surroundings it attains maturity and explodes 

 shortly after sunrise ; but if kept in a room where 

 there is little or no sunlight the explosion does not 

 take place until midday or later, and sometimes not 

 at all. This would seem to show that not only 

 elasticity of the tissues but also light is a great factor 

 in causing the projection of the spores, which has 

 been variously attributed by different writers to 

 divers other causes, and erroneously to the tension 

 caused by the liquid in the stem. But if this were 

 the case, then heat would favour the explosion, 

 causing expansion ; but experience shows that it is 

 just the contrary which occurs. 



The natural size of this little fungus is about 

 three millimetres ; hence it will be found rather tiring 

 to examine with the naked eye, but with a good 

 magnifying glass, giving eight or ten diameters, one 

 can study all its movements with ease and comfort. 



One must be careful not to confound it with an 

 allied species, Pilobolus oedipus, which it closely 

 resembles, and which may be found in the mud and 

 slime of gutters ; but in this latter species the spores 

 are globular and of a larger diameter than those of 

 Pilobolus crystallinus. 



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