Page:Encyclopædia Britannica, Ninth Edition, v. 9.djvu/864

 828 FUNGUS carcinomatis, and pits are of constant occurrencD in corre sponding cells of the Lycoperdaceae, and in the filaments which bear the fructification of Dactyl ium. Chemical analyses of the cell-membrane show that it possesses the elementary constituents of cellulose ; but since the uncoloured and uuthickened membrane does not com monly exhibit the characteristic reaction of cellulose to wards iodine (neither simply nor after treatment with potash or Schultz s mixture), nor towards many of the reagents commonly employed in testing typical cellulose, it is neces sary to apply to it the special term fungal cellulose. In several special cases, however, typical cellulose is known to exist. The membranes of old cells frequently undergo a kind of lignification, and in this condition offer extra ordinary resistance to such treatment as that with concen trated sulphuric acid. The Cell-Contents. The protoplasm of fungal cells has no special quality of importance to distinguish it from that of other vegetable cells. Professor Sachs states (Bot. Ztg., 1855) that under his observation the apices of growing hyphas seemed to consist of one mass, in which the mem brane could not be distinguished from the protoplasm ; but Professor De Bary (Morp. u. Physiol. der Pilze, &c.), on the other hand, finds that the same conditions as exist in similar situations in other plants obtain here, viz., a dense mass of protoplasm enclosed by a tender membrane an experience endorsed by most mycologists. The existence of a nucleus was long denied, and indeed its presence in the cells of the thallus has not yet been proved ; but in the reproductive organs, where it had long been overlooker!, its occurrence is not uncommon. Attempts to prove its existence in the cells of the thallus have not been wanting, but as yet with apparently no success : Schacht s observations on this head are notably untrustworthy, since there is no doubt that he confounded the true nucleus in other fungal cells with drops of oil and such bodies. The formation of vacuoles takes place as in other vegetable cells. Oleaginous matter is present, often abundantly, in nearly all fungi, in the form of drops of various sizes. Water (cell-sap) is necessarily present, though the quantity varies considerably without serious injury to the plant. A good proof of this variation is to be found in the expansion or contraction of the fila ments of many Hyphomycetes according to the supply of water. In fungi with firmer cell-membranes, air-bubbles take the place of the water which has evaporated, and the contraction of the hyphse is very inconsiderable. The fungal cell is wholly destitute of chlorophyll, and, it may be safely stated, of starch also. Schlossberger and Diipping record their detection of starch granules in the extracted sap of Cantkarellus cibarius ; but from their method of investigation it is highly probable that these were accidentally present. The pigments of various colours to be found in many fungi are perhaps in most cases properties of the cell- membrane. Another class of them is peculiar to the cell- contents, and a third seems to pervade both membrane and contents. Those peculiar to the contents are mostly of an oleaginous or resinous nature, and their occurrence is in the form either of minute particles distributed throughout the protoplasm, or of larger drops or granules scattered irregu larly among the contents. From the pigments peculiar to the fungal cell there are to be distinguished those absorbed in an unaltered state from the substratum. An instance of this is to be found in Peziza (eruyinosa, which owes its colour to the abnormally greenish wood on which it grows. It was long thought that the Peziza was the cause of the green colour, but a sufficient proof is contained in the facts that the wood is more frequently found green without any trace of the fungus than with it, and that the upper part of the fungus is sometimes uncoloured when the lower portion has become green. Moulds, and other fungi usually colourless, are occasionally stained with the colour of an unusual substratum. The subject of the pigments of fungi is one of which our knowledge is very incomplete. Crystals of calcium oxalate are to be met with on the surfaces and in the intercellular spaces of many of the larger fungi ; but in only two cases have they been found in the interior of the cell (Phallus caninus and Russula adust a). Cell-division takes place in the same way as in other plants. The mycelium is the part of the thallus devoted to the functions of absorbing and storing nutriment. It consists of hyphae developed directly from the germinating fila ments, but often on further growth intricately bound up (fre quently anastomosing) with each other, usually in amorphous masses, but sometimes in more or less definite bodies. In the larger fungi a number of hyphaa (in which case they run parallel to each other) are sometimes associated into bundles, like rootlets. The mycelium not nnfrequently persists for several years. Mycelia in general bear so strong a resem blance to each other that it is usually impossible to determine the species to which they belong on their own characters. A number of parasitic fungi possess peculiar organs called haustoria, which perform the function of extracting nourish ment, and when necessary retaining the plant in its posi tion. These are lateral branches of the mycelial hyphse of various shapes and sizes. In Erysiphe, the mycelium of which creeps over the surface of its host plant, the haustoria are emitted abundantly from the side of the hyphse next the epidermis, into which they penetrate and cause decay. They are in this case small and irregular in shape. On the Peronosporece, the mycelium of which inhabits usually the intercellular spaces of living plants, haustoria are frequently present. In some cases, as in Cystopus candidus, they have the form of minute stalked globules, but in most other Peronosporeaj they are irregular filamental protuberances, frequently branching to such an extent as almost to fill the affected cell. Sclerotia are tuberous bodies composed of densely inter woven mycelial hyphse enclosed by a layer of pseudo-paren chyma. They are specific in occurrence, like the bulbs and tubers of phanerogams, and are situated on or beneath the surface of the substrata the ground or parts of plants. They were long regarded as independent forms of fungi, but it has been discovered that they are only resting states in which nourishment is stored up. They vary much in size. The Receptacle. On the mycelium there arises a body called the receptacle, the function of which is to bear the reproductive bodies, the spores. It varies much in size in different fungi ; in most cases it forms the greater part of the whole thallus, and in others it consists of a simple or branched hypha. The same species of fungus may possess more than one kind of receptacle, either in different genera tions, or arising subsequently from the same mycelium. According to their structure receptacles may be divided into two groups, viz., those which consist of one hypha, and those which, composed of aggregated hyphre, form a com pound body. In certain cases the receptacle is entirely sup pressed (as in the interstitial oogonia of the Peronosporeoe). When the receptacle consists of a simple or branched hypha, the spores are borne terminally. The sporophorous hyphse are branches of the mycelium, rising usually vertically from it, and themselves frequently so characteristically branched as to afford means of generic and specific distinction. After bearing the first spore, the sporophore may again grow for a short space before bearing another. In compound recep tacles the fructiferous hyphse form together expansions