BIOLOGIC PRINCIPLES ILLUSTRATED BY FUNGI. Some general biological principles are admirably illustrated • by the fungi. Probably no other of the lower plants are so varied in their adapta tion to special life conditions as are the fungi. The fact is shown by the immense number of species, for the fungi are far more numerous than the alga, and they present more varied methods of asexual reproduction than does any other group of plants. Besides the specialized spores for rapid distribution, there are devices by which the protoplasm of the fungus may at any time pass into a resting state, and so survive un favorable conditions. When the entire plant body is affected, the resting condition is called a sclerotium, and if small portions are so spe cialized they are called chlamydospores. As would be expected, the development of a large number and variety of reproductive conditions makes possible very complicated life histories (polymorphism), and in this respect the fungi arc the most remarkable of all plants. This astonishing development of polymorphism, with its varied and specialized reproductive phases, is directly traceable to the parasitic or the sapro phytic life which a fungus must always lead. The evolutionary influences work constantly toward the special and successful adaptation of the parasite to the host in the one case, or of the saprophyte to its particular nutrient sub stances in the other. The result of fungal evolu tion is necessarily immense diversity, shown not only by the number of species, but also by the wonderful variety of things that fungi can do. Species of Bacillus among the Bacteria have a general similarity of form and structure, but some are mere saprophytes, concerned only with some phase of decomposition, and others are parasites in the higher animals, even man, and are there the cause of subtle diseases. It is im portant to note that the life of fungi has led to the degeneration of sexual organs, and finally to their entire suppression. Yet some of the groups in which sexuality is entirely lost are the most successful in establishing themselves, as is ex emplified by the toadstools and rusts.
In conclusion, the .conception of the fungi should be an immense assemblage of parasites and saprophytes with several points of origin from differed stocks of the alga, and branching out into innumerable species, each adjusting it self to the peculiarities of a life leading to con stant specialization. There can be, in evolution of this character, no general structural results, such as are exhibited, for example, by sexual evolution and by the differentiation of the sexual (gametophyte) and sexless (sporophyte) genera tions among the algae by the increasing im portance of the sexless generation through the mosses and ferns, and by heterospory and the reduction of the sexual generation (gameto phyte) in certain fern-plants and in all the seed plants.
For general treatment of the fungi, consult: Engler and Prantl, Die naturlichen familien (Leipzig, (Leipzig, 1887) ; De Bary, Comparative Morphology and Biology of the Fungi, Mycetozoa, and Bacteria, translated by Garnsey (London, 1887) ; Zopf, Die Pilze (Breslau. 1890) ; von Tavel, Vergleichende Morphologic der Pilze (Jena, 1892). Some special works are listed in the articles on the various groups of fungi.
Fossil, FUNGI. Although fossil remains of fungi are sufficiently common to indicate that these plants were important members of the floras of all periods from the Carboniferous to recent time, comparatively little has been done toward studying them, and the sum total of our knowledge of fossil fungi is small. There seems to be no great difference between the ancient and the modern forms. The earliest known fossil fungi have been described as Peronosporites from the Silurian system. They occur as mycelial threads with frequent bulbous expansions in limestones of the Clinton series in western .NeW York, and were detected in thin sections of the rock that were being studied under the micro scope. The Carboniferous fungi consist largely also of mycelia, referred to the same genus Peronosporites, the threads and bulbs of which have been found in the stems of Lepidodendrons from the British coal measures. Similar forms have been found in fossil fruits (carpoliths) from the coal measures of France.
The Tertiary deposits have afforded many fossil fungi. The silicified woods of Egypt, Eu rope, and North America contain many species.
Fossil leaves from the Tertiary shales and sand stones often bear patches of the parasitic As comycetes, which are very difficult to study in the fossil state. The leaves in amber also carry Ascomycetes, and amber insects infested with mucorine fungi have been found. Toadstools, and other members of the Hymenomyeetes, are rarely represented in rocks of Tertiary and post-Ter tiary age. They appear in the Tertiary lignites of Europe and North America, with the genera Hydnum, Lenzites, and Polyporus. Interesting, though indirect, evidence that toadstools and similar forms were far more abundant during the Tertiary times than is indicated by their meagre fossil representatives, is afforded by the fact that large numbers of fossil beetles and flies found in the rocks of that period belong to genera which at the present time are wholly fungus eaters.
Consult: Zittel, Schimper, and Barrois, Traite de paleontologic, part ii.; Paleophytologie (Paris, Munich, Leipzig, 1891) ; Solms-Laubach, Fossil Botany (Oxford, 1891) ; Loomis, "Siluric Fungi from Western New York," in Bulletin of the New York State Museum, No. 39 (Albany, 1900).