Cereals, wheats and grasses, suffer from other well-known forms of microscopic fungi termed rusts and smuts, which cover the blades or infect the full ear of the fruit. The name given indicates their colour, and these belong, for the most part, to the genus Uredo and the family of the Basidiomycetes. They have no endogenous spores but as many as four forms of exogenous. This is also the case with wheat and barley, whereby they are distinguished as Uredo or Puccinia graminis (see Figs. 273 and 274, and [Plate I]., Nos. 19 and 22, Æcidium berberidis). For a long time it was believed that Uredo linearis and Puccinia graminis were so many distinct species, but it is now known that there are only three successive phases of the developmental stages of a single species—that, as a matter of fact, puccinia presents the phenomenon of alternation of generations, that is, that the complete development of the fungus is only effected by its transference from one plant to another. Other uredines, Ustilago and Tilletia smuts, are more apt to affect the ears of wheat, rye, and other grasses than puccinia. Bread made from wheat affected by smut has an acrid and bitter taste, while that made from rye flour often produces a serious form of disease. The propagation of either, then, should be stopped as quickly as possible by destroying all barberry bushes growing near or within the vicinity of corn fields, and by other means. The ergot of rye is due to distinct species of fungi having endogenous spores enclosed in a sac or ascus, hence the name of the family, Ascomycetes or Tuberaceæ, which are reproduced by the spores contained in these asci. Truffles belong to this family. But other members of the same family have several forms of spores, and these again present us with the phenomenon of alternation of generations.
Fig. 276.—Fungi, Moulds.
p. Spores of Tilletia caries; q. Spores of Tilletia caries, when germinating, produce a fœtid olive-coloured spore in cereal grains; r. Telentospores of Puccinia graminis; s. Crystopus candidus, spores growing in chains; t. Petronospora infestans, mildew of turnips, &c.; u. A transverse section of ergot of rye, showing spores in masses; v. Claviceps purpuræ, associated with ergoted rye.
Ergot of rye is used in medicine, but if not used with care it will produce a dangerous disease. This parasitic fungi consists of minute microscopic masses of spores, which cover the young flower of the rye with a white flocculent mass, formerly termed sphacelium. The mycelium formed spreads over the ear of corn in thick felt-like masses, termed sclerotis. The sphacelium changes its form in the following spring. Other changes are brought about, and it seems to pass through a cycle of alternations of generations.
Bread made from rye so infested is known to produce grave consequences, soon to become fatal if not detected in time. The disease is termed ergotism, and gangrene of the extremities takes place among people of the north of France and Russia, who consume bread made from rye flour. Ergot of maize will also cause similar diseases. Fowls and other animals fed upon this cereal become in a short time poisoned, and the cause of death is not rightly suspected. There is another fungus belonging to the same group of Ascomycetes, known as Eurotium repens, which appears upon leather when left in a damp place, and also upon vegetable or animal substances if badly preserved, and gradually destroys it. This mould is of a darkish green colour.
The minute spores display themselves as rows of beads when fully ripe on the erect mycelium. Aspergillus glaucus represents the white exogenous spores of the sphacelium of the ergot of rye; and those subsequently produced in the yellow balls correspond with the asci developed in sclerotis, the endogenous species. Many of the parasitic species belonging to the genera Erysiphe, Sphæria, Sordaria, Penicillium, &c., have a similar mode of propagation, and affect a large number of plants.
Parasitic Fungi of Men and Animals.
In the microscopical examinations especially given to the elucidation of parasitic diseases of the skin, previously referred to, I discovered more varieties of spores and filaments of certain cryptogamic plants associated with a larger number of specific forms of fungi than any previous observer. I did not, however, feel justified in concluding, with Küchenmeister, Schœnlein, and Robin, that these fungoid growths were the primary cause of the diseases referred to. Indeed, the foremost dermatologists of the period utterly refused to entertain the specific germ theory of the German investigators. Nevertheless, I contended, “the universality of their distribution is in itself a fact of very considerable importance, and one pointing to the belief that they are scavengers ever ready to fasten on decaying matter, and, on finding a suitable soil, spread out their invisible filaments in every direction in so persistent a manner as to arrest growth and overwhelm the plant in destruction.”[53]
Special forms of fungi are given in [Plate I]., Nos. 10-14, and those of the ascomycetes in Nos. 17-21.