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 hyph, 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 Willkommit, 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, among the fresh green shoots, individual branches are to be seen bearing golden- 
yellow needles. Towards autumn, scarlet cup-shaped fructifications make their 
appearance upon the surface of the bark on the branch; in the 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 the 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 ferns; whereas a considerable number of parasites 
settle upon lichens and even on the fructifications of fungi, moulds even 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 pups® of butterflies and other insects, and its relatively very large 
fructification at length bursts out of the body 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 in 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 hoary 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 Musce, 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 by a whitish halo, and this 
is composed of a conglomerate of spores thrown off 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 
