The Sphæriacei, another order of Ascomycetes, are enormously numerous. There are 1,000 well known species of this order, and probably twice as many undetermined; for there is scarcely a twig or dry branch in the forests, hedges, or gardens on which they may not be found. The rose tree, the oak, and other plants harbour more than one species at a time. The genus Cordyceps and many so-called species of Sphæria are only the ultimate development of fungi of other families. The Cordyceps purpurea, discovered by M. Tulasne on the ergot of wheat, has a short, upright, slender stem, with a minute pale purple globose fruit-bearing head. In this ergotized state the white substance of the grain is converted into a firm mass without any appearance of meal, and having very powerful properties. When sown, it is found to produce the Cordyceps. Mr. Currey found the same plant on the ergot of the common reed, and there are several other species of Cordyceps, all of which are only the second form of ergot. To these may be added the Cordyceps militaris of Ehrenberg, already shown (p. [283]) to be the ultimate development of the Isaria, which attacks the caterpillars of the bramble moth; and the Cordyceps Robertsii, which grows like a bunch of rushes from the head of the Hepialus virescens of New Zealand; whilst a kind of wasp in the West Indies, which continues to fly about after it is attacked, is at last killed by branching Cordyceps, which project from its head like a pair of antlers. But the largest of all these parasites grows on an enormous larva found on the banks of the river Murrumbidgee in Australia. It appears that species of Sphæriæ are parasitic on insects of very different affinities in China, America, and Europe. It may be presumed that, like the Cordyceps militaris, they are the ultimate development of fungi belonging to other families.
Fig. 36. Sphæriacei:—Sphæria Desmazierii; a, ascus; b, sporidia; c, mycelium with conidia. Mucedines:—d, Botrytis curta.
In the genus Sphæria the fungus springs at once from its mycelium, and consists of a perithecium or external case, to the internal walls of which the asci are fixed. Each ascus contains eight sporidia or spore cells, and when the fruit is ripe the asci are emitted through a pore or slit in the perithecium or external coat. [Fig. 36] represents the fructification of Sphæria Desmazierii. Sphæria bombarda is like an assemblage of minute black beads lying flat and crowded together upon decayed wood; each bead is an oblong vesicle pierced at the apex for the emission of the microscopic sporidia, or spore cells. The Sphæria aquila, found upon decayed wood, has its fruit-bearing vessels seated upon thickly matted fine threads. In some species they are in tufts; others have bottle-shaped perithecia sunk into the stems of the berberry, laburnum, and decayed oak palings; and lastly the candle snuff Sphæria may frequently be seen like patches of soot at the bottom of stakes or gate posts. More than two hundred well ascertained species of the genus Sphæria are native in Great Britain alone.
The genus Nectria, which forms a connecting link between the genera Peziza and Sphæria, has several interesting species, as the Nectria Peziza, which grows in a congeries of most minute cups forming a bright orange-coloured patch on decayed stumps of trees.
In the order Perisporacei the perithecia, or external cases, are free and become dehiscent at last, but when young these fungi consist of cellular jointed filaments like necklaces, rising upright from their mycelia, and bearing reproductive bodies. In this state they constitute the mildew on the vine, rose tree, turnip, hop, pea, &c. They are true parasites, appropriating the juices, and filling up the breathing pores of the leaves, so as to cause disease and often death. The vine mildew, which has been called Oïdium Tuckeri, but which is now supposed to be an imperfect state of Erysiphe, never advances beyond this state, consequently it never has more than one form of fruit. Mr. Berkeley has discovered that, on the contrary, the hop and pea mildews, which belong to the genus Erysiphe, have five different modes of reproduction. The destructive power of these fungi is strongly illustrated by the extraordinary energy of their mycelia in draining the vital juices of the plants on which they live in order to form such various kinds of fruit; and the quantity of fruit produced is so enormous, that if the whole were to germinate no genus of plants for which they have an affinity could escape annihilation. Other species of Erysiphe have at least three different modes of reproduction. The perithecia of some of these fungi are beautiful objects for the microscope.
The Physomycetes, which form the sixth and last order of the great fungus family, have bladder-like fertile cells scattered on threads, the number of sporidia within the cells being indefinite. The Antennariei are dark coloured felt-like fungi which run over the leaves of living trees, and have fruit on black threads, which in some species, when magnified, resemble the antennæ of certain beetles. The species of this order are not common in Britain, and they are supposed to be only a condition of some other fungi. They are certainly spore-bearing plants, yet the fruit-bearing cells of the Antennaria Robinsonii sometimes contain a ready formed miniature of the parent plant waiting to be set free,—a singular analogy between these microscopic fungi and flowering plants.
The order Mucorini, or moulds, has threads springing from the spawn, bearing on their extremities large vascular sacs containing asci with spore cells. The genus Ascophora contains several remarkable species, as Ascophora elegans, which has two kinds of fruit, and attacks bread while yet hot from the oven: however, the spores were probably in the dough, for it has been ascertained that the spores of some of the lower fungi retain their vitality after being exposed to the temperature of boiling water. The Mucors are probably found on decayed and decaying matter all over the world; they grow on fat, on greasy walls, and on decaying fruit and vegetables.
The extreme minuteness of the reproductive bodies of the microscopic fungi, many of which are not more than the 20,000th part of an inch in diameter, and their extraordinary and varied forms even in the same plant, have made these fungi one of the most difficult studies in the whole science of botany. There is still some obscurity with regard to those minute motile bodies supposed to be male particles, and their analogues, which have not been seen, or have rarely been seen to germinate. These bodies have been observed in comparatively few genera, and nothing more than mere molecular motion has been observed in them.
One of the most unaccountable circumstances in the history of the lower fungi is their sudden appearance in immense numbers, and the rapid extension of disastrous and destructive epidemics caused by them among plants and animals, as the potato murrain and the vine disease, which, though widely spread through Europe and Madeira, leaves the North American vines unscathed, whether grown at home or abroad. The black mildews at one time raged so much in the Azores and Ceylon as to threaten the complete annihilation of the orange and coffee plantations. Their ravages have been scarcely less among the olive trees in some parts of Europe; and the Lanosa nivalis, which grows in the melting snow in spring, is supposed to be the cause in many instances of the death of the germs of the sprouting rye. The destructive course of most of these has abated, but the silkworm disease still continues. The fungi require warmth and a moderate degree of moisture for their development, but the unwonted multitudes in which the parasites occasionally appear, possibly indicate some meteoric influences of which we are ignorant.