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.