In responding to the spore-case has ceased to produce swimming spores, but has become itself an aërial reproductive cell (conidia, q.v.). the water-molds (Saprolegniales) sexuality has so degenerated that the male organs, although frequently present, are rarely, if ever, functional. The Chytridiales include many one-celled forms whose life history presents a continuous alternation of motile and non-motile conditions, remind ing one of the life histories of some of the green slimes (Protococcales) among the algae. It has been suggested that the Chytridiales have come from the Protococcales, a group of alge much lower than the ancestors of the downy mildews and the water-molds. It is possible, however, that the Chytridiales are degenerate forms of higher fungi. The common black molds (Mucorales) have less of the algal characters than other Phycomycetes, but the terminal spore-cases and sexual organs recall the downy mildews. The Entomophthorales are a highly specialized group of insect parasites whose relationships are very obscure. natural groups, so that species are constantly being removed from this artificial assemblage. BASIDIOMYCETES. The Basidiomycetes (mushrooms, toadstools, etc.) are a remarkable class. There is no trace of sexuality in the group, not even the vestiges of sexual organs which generally remain even when plants reproduce without them. Apart from certain peculiar phenomena of fusing nuclei, there are no clews to the problem of the origin of the group. The diverse orders are held together by a phase common to all the life histories, namely, the basidium, which is the swollen tip of a filament bearing spores on slender branches. It has been found that this basidium of the toadstools and the puffballs is represented by the promycelium of the smuts (Ustilaginales, q.v.) and rusts (Uredinales, q.v.). This promycelium arises from the winter spore (teleutospore), which is essentially only a resting spore to tide the parasite over an unfavorable season. There are kinds of rusts (Leptopuccinia) in which the teleutospores form promycelia directly upon the host plant, and these conditions resemble strikingly the basidia of certain toadstool forms. The winter spore (teleutospore) of the rusts and the smuts is then merely an adaptation related to the parasitic habit, and unnecessary for saprophytes such as the toadstools, bracket fungi, and puffballs. It must not be supposed, however, that there is only one conspicuous line of development among the Basidiomycetes, for there are several divergent lines, prominent among which are the rusts (Uredinales), smuts (Ustilaginales), and certain orders of the toadstools (Hymenomy. cetes), and puffballs (Gasteromycetes). The relation of the Basidiomycetes to the other groups of fungi is problematical. The SACCHAROMYCETES. The group Saccharomycetes (yeasts) is a very problematical one. fact that the spores of many fungi pass into yeast conditions when placed in the proper nutrient solutions, suggests the derivation of this interesting group from one of several sources. In a sense the yeasts are degenerate forms, for they have adopted a simple life history and morphology, but physiologically they are highly differentiated. ASCOMYCETES. The Ascomycetes (sac-fungi) present structures and life histories that are very difficult to correlate with those of the Phycomycetes. Some of the lower forms are undoubtedly sexual. There is present a female cell (ascogonium or archicarp) fertilized by a discharge from a neighboring male cell (antheridium), the condition recalling at once that in the downy mildews. The fertilized female cell, however, develops a special system of filaments that finally produce the characteristic spore-containing sacs (asci). These filaments are generally associated with sterile portions of the original body to form a fructification called the ascocarp. The ascocarp may be compared to a similar growth (cystocarp) produced from the fertilized egg of the red alga (Rhodophyceae). The subject becomes further complicated, however, by an apparent tendency among the Ascomycetes to give up sexuality. In some higher groups repeated investigations have failed to demonstrate sexual organs, and the ascocarp in consequence probably develops without a sexual act. There have been attempts to homologize the ascus (spore-sac) with the sporangium (spore-case) of the black BIOLOGIC PRINCIPLES ILLUSTRATED BY FUNGI. molds, assuming that the large and variable Some general biological principles are admirably number of spores in the latter structure became illustrated by the fungi. Probably no other of reduced and fixed to eight, the usual number in the lower plants are so varied in their adaptathe former. Later studies upon the development tion to special life conditions as are the fungi. of the spores, however, indicate that the two The fact is shown by the immense number of structures are not related. It is then possible species, for the fungi are far more numerous than that the ascus is a special form of spore-case pe- the algæ, and they present more varied methods culiar to the Ascomycetes. There are a number of asexual reproduction than does any other of peculiar forms of spores in the Ascomycetes, group of plants. Besides the specialized spores developed at various periods in the life history, for rapid distribution, there are devices by which manifestly for purposes of distribution. They the protoplasm of the fungus may at any time have been named conidia, pycnidia, etc. There pass into a resting state, and so survive unare a great many fungi known only through favorable conditions. When the entire plant some fructification of this character. For con body is affected, the resting condition is called venience they are placed in a group called the a sclerotium, and if small portions are so speHyphomycetes or Fungi Imperfecti. Most of the cialized they are called chlamydospores. Hyphomycetes are believed to be imperfect forms would be expected, the development of a large of Ascomycetes, but among them there are also number and variety of reproductive conditions large numbers of species that undoubtedly be- makes possible very complicated life histories long to other groups. There are practical rea- (polymorphism), and in this respect the fungi sons for this artificial group, as many of the spe- are the most remarkable of all plants. cies are economically important. Studies in their astonishing development of polymorphism, with life histories are constantly bringing to light its varied and specialized reproductive phases, is phases which determine their place among the directly traceable to the parasitic or the sapro As This 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 substances in the other. The result of fungal evolution 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 important 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 exemplified 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 different stocks of the algae, and branching out into innumerable species, each adjusting itself to the peculiarities of a life leading to constant 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) generations 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 (gametophyte) in certain fern-plants and in all the seedplants. For general treatment of the fungi, consult: Engler and Prantl, Die natürlichen Pflanzen familien (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 Morphologie 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 microscope. 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, Europe, and North America contain many species. Fossil leaves from the Tertiary shales and sandstones often bear patches of the parasitic Ascomycetes, 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 Hymenomycetes, are rarely represented in rocks of Tertiary and post-Tertiary 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 funguseaters. Consult: Zittel, Schimper, and Barrois, Traité de paléontologie, part ii.; Paléophytologie (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). FUNGI, ECONOMIC. Species of fungi that may directly or indirectly affect man's welfare. Of those that affect man directly, the edible and poisonous species and some parasites, such as ringworm, barber's itch, etc., may be mentioned as examples (see FUNGI, EDIBLE AND POISONOUS; MUSHROOM; TRUFFLE); of those that affect him indirectly are plant diseases, molds, some animal diseases, etc., whose functional activity may result in monetary or some other kind of loss. A large majority of fungi (saprophytes) are capable of living only on decaying organic matter, and since they do not ordinarily attack living plants, they do not produce plant diseases. They are therefore of little economic importance except as they occur on fruits and other foodstuffs, timber, clothing, etc., when they may be considered harmful. On the other hand, many of these organisms are more or less beneficial, since they act as scavengers in the destruction of organic matter which would long cumber the earth if dependent upon the slow process of chemical oxidation. Under abnormal conditions of moisture, temperature, etc., some saprophytic fungi (usually called facultative parasites) are able to attack and injure living plants. The parasitic species (another large group) occur normally upon living plants and animals, from which they derive their sustenance. The plant or animal upon which they live is called the host. The relationship between host and parasite is more or less intimate, and as the economic plants are affected, the importance of the parasite is the greater. In some cases the fungi are of positive benefit to man because they (entomogenous fungi) destroy noxious insects, as locusts, grasshoppers, flies, scale-insects, etc.; others live at the expense of fungi that are themselves injurious to plants of value to man, as in the case of Darluca filum, a parasite of the injurious asparagus rust. The number of fungi that attack living animals is large, and in some cases the attack is very destructive. Young fish in hatcheries are subject to diseases due to fungi; and higher animals often suffer similar attacks. A lung disease of horses is caused by the presence of the fungus Botriomyces, and the |