Page:Encyclopædia Britannica, Ninth Edition, v. 9.djvu/865

 FUNGUS 829 called hymcnia, from which the individual fertile branches arise. If the hymemum is formed upon the exterior surface of the receptacle it is termed gymnocarpous, and if within the receptacle angiocarpous. The hymenium never pro duces any but asexual spores. Reproduction. The reproduction of fungi u effected by both sexual and asexual means the latter being far the more frequent of the two. No one species is known to possess more than one form of sexual reproduction, though it is frequently the case that more than one kind of asexual reproduction belongs to it. In many fungi no sexual re production is known to exist, but it is generally believed that in such cases the plants are merely members of a cycle of generations, the other stages in their life-history being unknown or unrecognized. The term spore is applied to all reproductive bodies, whether asexual or the product of the union of sexual cells. Discussion has frequently been engaged in as to the propriety of employing the same term to denote both kinds of bodies ; but though in isolated c ises the use of new terms has been advised, no satisfactory system of nomenclature has been established. There is, however, no doubt that some distinction ought to be made. Sexual reproduction is effected by the union of two cells of different nature, which in themselves are incapable of farther development. In the usual forms these cells are apparently of different nature, but in the phenomenon of conjugation the difference in the sexual elements is not de- terminable, though doubtless existing within the molecular sphere. The product of the union of sexual cells is de veloped into an organ of reproduction which, at the proper tim3, fulfils its office by giving rise either to a new mycelium directly or to a receptacle. These organs of reproduction bear names more or less expressive of their nature, such as zygospore, oospore, &c. In those fungi of which the life-cycle is known, several different kinds of asexually produced spores have been observed. In only one group, the Phycomycetes, are motile spores (zoospores) known. In all other cases they are produced either at the apex of a basidium (basidio- spores) or similar sporophore (conidia, &c.), by cell-division, or within an ascus by free cell-formation (ascospores). In compound or septate spores, which are multicellular, each separate secondary cell is termed a merispore. Gemma; are produced by the breaking up (by cell-division) of hyphce into series of cells capable of germinating. The germination of spores is dependent chiefly on moisture, but to their farther development specific conditions are necessary, a description of which is beyond the scope of this article. The dissemination of spores is effected chiefly by the agency of the atmosphere and of water, and it is probable that insects or other animals have very little to do with it. In their mode of life fungi are controlled by the absence of chlorophyll. Without it they cannot assimilate, and are therefore driven to obtain their nourishment by taking up the carbon compounds assimilated by other organisms. Their modes of life are either parasitic or saprophytic. As parasites they inhabit the bodies of living plants and ani mals, and even of other fungi. In some cases they kill their hosts, and in others encourage growth, as in the case of the Lichenes; and between those two extremes various degrees of parasitism occur. As saprophytes they promote the decomposition of dead organic bodies, and thus aid in the production of carbonic acid, water, and ammonia, the elements of which return to the course of organic life. Jodin states that some fungi absorb as much as 6 per cent, of their nitrogenous contents in the form of nitrogen gas from the atmosphere. In the decomposition of fungi am monia is formed from the nitrogenous compounds. As parasites and saprophytes their influence as regulators in the economy of nature may be compared with that of the lower animals living the same mode of life. Though the ravages of parasitic fungi are mostly confined to the vegetable kingdom, it is well known that many animals suffer from their attack. The occurrence of para sitic fungi on insects and fish is common ; more rarely do they attack the higher animals or man. It has been strongly contended that the minute fungi play very import ant parts in many diseases of man, but this has usually been much exaggerated. The occurrence of Bacteria on the mucous surfaces of living bodies and on wounds has given rise to much discussion; and there is no doubt that insufficient knowledge of these organisms has often led to error, the observers not unfrequently mistaking the products of the decomposition of organic bodies, crystalline precipitations, &c., for Bacteria. It may safely be maintained that these are ot tener the concomitants than the causes of disease in man. A considerable number of fungi have also been described as playing active parts in various skin-diseases, but very little trustworthy information about their life-history has ever been gained. The economic properties of fungi are of an unimportant character. A great number are poisonous, and many are edible ; a few are used for medicinal purposes. Many of those described as edible, though they can be eaten without any serious consequence, are certainly not likely to become articles of food. At the same time it may be mentioned that much valuable food is annually lost through ignorance of the excellent esculent qualities of a few common fungi. The phosphorescence or luminosity observed in several fungi has given rise to many absurd conjectures, This phenomenon depends on the respiration of oxygen, those fungi which exhibit luminosity ceasing to do so when the oxygen is extracted. Geographical Distribution. From the extreme poverty of our knowledge of the geographical distribution of fungi no general estimate can be even outlined. Of the fungi of by far the greater portion of the world we have no account, or at the best the meagre collections of passing explorers. Of even the European mycologic flora our knowledge is far from complete, Russia, Turkey, Spain, Portugal, and even Ireland, being only partially examined. Of countries in which the surveys have been more complete, only England, Scotland, Wales, Germany, France, and large districts of Austria, Italy, and Switzerland can be pointed to. Of the whole American continent the Carolinas alone are tolerably well known, and though collections hnve been made in Mexico, Texas, the island of Cuba, and a few tracts of South America, the examination of these countries has not been thorough. China, Japan, Siberia, and Further India are totally unexplored; but, on the other hand, Ceylon and the northern part of India are perhaps as well known as any other extra-European district save Carolina. From the Himalayas and northern India there are the collection and notes of Sir Joseph Hooker. In Africa, Algeria and the Cape have been examined, but from the tropical parts of that continent we have only the collection and notes of Dr VVelwitsch, which are, however, of great value so far as the district he explored extends. Any attempted scheme of geographical distribution would, therefore, be not only incomplete but open to great error, from the very partial accounts from the most of those dis tricts which have been examined. As in other vegetables, heat and moisture necessarily exert the greatest influence on growth, and therefore on distribution. The character of the trees composing the forests of different countries, and the amount of cultivated land, subordinately affect the nature, if not the numbers, of the fungi inhabiting them. One broad principle, however, seems apparent, viz., that the large fleshy fungi, like the Agaricini, affect temperate countries