Ferments may be formed in the wort of beer, in the solutions of grape and cane sugar, in the juice of gooseberries, currants, &c., by means of the submerged spores of the Uredines segetum and Rosæ, of Ascophora elegans, Mucor Mucedo, Periconia hyalina and others. There are active exchanges continually going on between the contents of the globules of ferments and the exterior liquid, and therefore a continual chemical action.[[59]]
M. Pasteur’s experiments on the nourishment of the Mucedines concur with the observations of others in showing that these plants are the origin of all fermentation properly so called. When he put a mere trace of the beer yeast fungus into pure water holding in solution the three crystallizable substances, sugar candy, an ammoniacal salt, and some phosphates, the globules of yeast were seen to multiply, deriving their nitrogen from the ammoniacal salt, their carbon from the sugar, and their mineral material from the phosphates; at the same time the sugar fermented. The same results were obtained from lactic yeast. M. Pasteur now sowed the spores of the Penicillium, or of some other mucedinous fungus in pure distilled water holding in solution the same ingredients, except that an acid salt of ammonia was employed to prevent the development of infusoria, which would soon have stopped the progress of the microscopic plant by absorbing the oxygen without which fungi cannot live. The result was the same as in the preceding case. There is consequently a complete analogy between the ferments, the mucedines, and plants of more complex structure. If in these experiments any one of the principles in the solution be omitted, the vegetation is arrested. The quantities of these substances in the air, the water, or in the spores themselves, are not sufficient to make up for the suppression of any one of them. For example, the carbonic acid in the air or water does not make up for the omission of the sugar. The mucedines and fungi generally obtain their carbon from their food and from rain water, for rain water holds in solution nitrates and ammoniacal salts together with salts of potash and lime, and M. Barral has ascertained the existence of phosphates also. M. Barral found that the nitrates and ammonia disappear under the influence of cryptogamic plants.[[60]]
In the genus Oidium, belonging to the Mucedines, the short threads have a string of spores, like a necklace of beads, on their tops. Species of this genus are found on damp paper and honeycombs; also on decayed oranges, and other spoilt fruits.
The family of the Ascomycetes produces spore-bearing cells, called sporidia, enclosed in long cylindrical sacs or asci, in the definite numbers two, four, eight, sixteen, thirty-two, &c. The great characteristic of this large group, consisting of six orders, is the fleshy soft texture and the more or less complete exposure of the fructiferous surface. In one division the asci are persistent; this includes the Elvellacei, the Tuberacei, the Phacidiacei, and the Sphæriacei. In the other division the asci are often evanescent, and this includes the Perisporiacei and the Onygenei.
The genera Peziza and Helvella are the principal fungi belonging to the order Elvellacei. The Pezizæ are a very numerous race, and consist of brilliantly coloured little cups, with or without stems, and more or less concave. They grow in the cooler part of the temperate zone, many show themselves in spring, and some of the largest and most beautiful appear during the melting of the snow.[[61]] A few are subterranean, and 128 species inhabit Great Britain, many growing on the ground, others on stumps of trees, dead sticks and timber, on living plants, damp walls, &c. They are singularly beautiful, including ‘many of the most elegant fungi, from the little white and red Peziza elegans, which is sprinkled over almost every fallen twig of the larch and other conifers; the pale toothed cups of the P. coronata, which abounds on the dead stems of herbaceous plants; the scarlet P. scutellata with its edge fringed with tawny hairs, and the graceful mouse-grey P. macropus, to the gorgeous P. coccinea, which attracts attention from its elegant form and bright colours; the more irregular, but not less brilliant P. aurantia, and the font-shaped P. acetabulum, which might form an elegant pattern for an architect or silversmith. Fifty others might be mentioned of equal pretensions to grace of form and brilliancy of colouring.’[[62]] Some of the genus are peculiar in their fructification, for in several plants of this group, besides asci containing eight sporidia, M. Tulasne met with cells full of eel-shaped particles like those in the Algæ, and although without motion he considered them to be analogous to the pollen of flowering plants. In the Peziza aurantia, however, the particles were staff-shaped and motile.
The genus Helvella may be regarded as Peziza with the cup inverted; consequently, it assumes the character of a pileus or hat, like a common mushroom, though often very different in shape, and, instead of spore-bearing gills, it has asci containing eight sporidia sunk in its fleshy texture. The pileus is ovate or mitre-shaped in some species and the margin free, in others it is more or less attached to the stem. When the pileus and stem are perfectly soldered together, we get the club-shaped species of the group.
Some obscure forms of this group, forming the genus Ascomycetes, cause the leaves of the peach, walnut, and pear to blister. They consist of little more than asci, accompanied by short necklace-shaped thread.
The Morchella esculenta, which is the morel, is so plentiful in some parts of England, that it is used for making katsup; while the Cyttaria, which is indigenous in the southern hemisphere, is the staple food of the Fuegians during many months of the year; its subgelatinous consistence indicates a nutritious principle. This species has the peculiarity of growing upon living branches, after the manner of the jelly-like fungus of the juniper.
M. Tulasne has discovered in Peziza, and in the genus Bulgaria and others, certain minute bodies, which he considered to be of the nature of the eel-shaped particles or antherozoids in the Algæ. Besides, he has shown that several species of Peziza have a second form of fruit. Fries had long before pointed out the identity of Fusarium tremelloides and the orange coloured Peziza common on nettle stems. Many of the larger Pezizæ and Helvellæ eject their sporidia with great elastic force. This is particularly remarkable in the Peziza vesiculosa, common in hot-beds, when the sun is shining; the least agitation raises a visible cloud of sporidia like vapour. The motions of the sporidia in the genus Vibrissea, which grows on twigs partly immersed in water, is very peculiar. They are exceedingly long and slender, and, when partly ejected, they wave about in the sunshine till they are expelled.
The fungi of the order Tuberacei are nearly all subterranean, and their fruit-bearing surface, as in the truffle, is internal. The asci are either irregularly deposited in cavities, or in the denser tubers they are sprinkled through a dark substance which is mottled with a paler tissue. The truffle, which is the most important and best known of the order, has a dark corrugated exterior, and the asci are represented by large pyriform sacs containing sporidia covered with a reticulated or spinose coat; but these spines are only the angles of continuous cells, and are beautiful microscopic objects. Truffles prefer calcareous soil, and a temperate climate. In England, they are found in Rutlandshire, and numerous species grow in Northamptonshire, but they are smaller than the continental truffles, which increase in abundance and size towards the south, and have their maximum in Italy, where they grow on the roots of trees and vines, and are hunted by dogs, or traced by the presence of a peculiar fly, and dug up for sale. Sometimes the dogs dig them up, to the annoyance of the proprietors of vineyards, from the mischief they do to the roots of the vines.