168 BACTERIA. FUNGI. 



invasion is limited in. extent, and the host succeeds in surrounding the area of 

 infection with a rampart of cells capable of resistance, and not liable to be pierced 

 by the hyphae, then the tree may live for years although its trunk is infested, and 

 in parts rotten. Such is also the case when particular branches of a tree are alone 

 attacked by the mycelium of a fungus. When, for example, the branch of a larch 

 is assailed by the mycelium of the Discomycete, Peziza Willkomrtiii, the fact is first 

 manifested externally by the fascicles of needles on the branch in question becoming 

 discoloured in the summer, and acquiring, prematurely, an autumnal appearance; so 

 that, amonof the fresh green shoots, individual branches are to be seen bearing- golden- 

 yellow needles. Towards autumn, scarlet cup-shaped friictifications make their 

 appearance upon the surface of the bark on the bi-anch: in tlie course of the next 

 few years the whole branch as a rule dries up, withers, and dies. It is then 

 broken by the first violent shock of wind and falls to tlie ground; but the tree, 

 disembarrassed of the dead bough, continues to grow unharmed, and to put forth 

 green shoots. It is only when almost all the branches of the larch are infested by 

 the mycelium of this fungus that the whole tree perishes as a result of the 

 invasion. 



Certain groups of plants are specially liable to be attacked by parasitic fungi, 

 and there are some conifers and angiospermous trees in which the same stem is 

 colonized by three, four, or five kinds of parasite. The green foliage leaves of large 

 numbers of flowering plants are also apt to be selected by parasites, as also are their 

 roots, tubers, and bulbous structures. Many parasites only attack the anthers in 

 flowers; others, as for instance the ergot, only the young ovaries. Parasitic fungi 

 are rarely found on mosses or fems; whereas a considerable number of parasites 

 settle upon lichens and even on the fructifications of fungi, even moulds being 

 infested by other fungi ; for example, a fungus named Piptocephalis Freseniana is 

 parasitic upon the very common mould, Mucor Mucedo. 



A fungus known by the name of Cordiceps militaris is parasitic in the cater- 

 pillars and pup» of butterflies and other insects, and its relatively very large 

 fructification at length bursts out of the bodj' infested by the mycelium in the form 

 of a club nearly 6 cm. long. This clavate structure, built up at the expense of the 

 insect's flesh and blood, produces tubular cells Ln special receptacles, and, inside 

 these, little rod-like spores, which afterwards fall out and infect other caterpillars, 

 developing within the bodies of these animals into a hoar}' mycelium and ultimately 

 causing their death. The disease of silk-worms, known as muscardine, is likewise 

 occasioned by a species of Cordiceps. We must also refer here to the widely- 

 distributed Empusa Muscce, a mould which attacks flies and causes every autumn 

 a regular epidemic amongst house-flies. The flies so often seen at that season 

 adhering stiff" and dead to window-panes are surrounded bj' a whitish halo, and this 

 is composed of a conglomerate of spores thrown oft' by the mould which is parasitic 

 upon the flies and causes their death. Parasitic fungi have also been observed in 

 the human skin, and recognized as the causes of skin-diseases. For instance, to the 

 mould Achorion Schoenleinii is due the disease of the skin popularly known as 



