FUNGI. 8l 



already been described, they form a group of objects closely connected together by 

 the history of their development, that is by their morphological characters 1 . The 

 Fungi are marked by the peculiar structure of the elements of their thallus. The 

 germinating spore developes into a branching tube with apical growth, which either 

 remains undivided by transverse septa, as is also the case in the Siphoneae, or 

 consists of cell-rows. These filiform fungal elements are called hyphae. It also 

 frequently happens that Fungi, whose hyphae are originally unicellular unseg- 

 mented tubes, form irregularly disposed transverse septa when they come to produce 

 organs of propagation. The unsegmented tubes in the Fungi as well as in the 

 Siphoneae have numerous nuclei; but more than one nucleus may also appear in 

 the cells of segmented hyphae. Among the Chytridieae, the simplest of the Fungi, 

 are species in which the vegetative body has not yet acquired the characteristic 

 hyphal structure, but is only a spherical or ovoid cell that soon turns to a zoospor- 

 angium. The higher forms of the same alliance (Rhizidium, Cladochjtrium, &c.), 

 on the contrary, have hyphae or elements very like hyphae. Deviations from the 

 filamentous form of the hyphae occur also in other Fungi. In the Yeast-fungus, 

 which consists of loosely connected branched rows of ellipsoidal cells and which 

 multiplies by sprouting (pullulation) (Fig. 71), a cell forms a small protuberance 

 usually at one end ; this enlarges to the size of the mother-cell, becomes cut off from 

 it by the formation of a dividing wall at the narrow point of junction, and finally 

 separates from it entirely. Sprouting occurs also under certain circumstances in 

 Fungi which have undoubted hyphae, such as Mucor, Empusa muscae. The Fungi 

 have been divided according to the character of their vegetative organs into Fission- 

 fungi (Schizomycetes, see above, p. 24), Sprouting-fungi (Yeast-fungi), and Spawn- 

 fungi including all forms with hyphal growth, but these characters will not supply 

 a general principle of division in any arrangement of the Fungi that keeps the 

 whole course of their development in view. 



The Fungi are either saprophytes and live on dead organic bodies, or are 

 parasites. But one and the same Fungus may live in both ways. Pythium De 

 Baryanum' 2 ', for instance, is a frequent and destructive parasite on the seedlings 

 of dicotyledonous plants, but it vegetates as readily in parts of dead plants or 

 animals. A considerable number of parasitic Fungi, among them Agaricus rnelleus 

 which lives on firs and other trees, have been successfully cultivated in suitable 

 solutions containing of course organic substances, while Fungi that under ordinary 

 conditions are saprophytes will in certain circumstances attack living plants; thus 

 the germ-tubes of Mucor, Pem'cillium, Bolrytis, &c., which cannot penetrate the 

 uninjured rind of such fruits as apples and pears, can spread as parasites in the 

 sound tissue of these fruits and bring about decay, if the rind is injured 3 . Other 

 Fungi, on the contrary, are strictly confined to the one or the other mode of 

 life. Pythium vexans, for instance, lives as a saprophyte in dead potato-tubers, but 

 is not able to penetrate into the tissue of the living plant 4 . Parasitic Fungi find 



1 Our knowledge of the development of the Fungi is due especially to the labours of Tulasne, 

 de Bary and his pupils. See also the literature cited below. 



2 De Bary, Zur Kenntniss d. Peronosporeen (Bot. Zeit. 1881, p. 521 ff.). 



3 Brefeld, Ueber d. Faulniss d. Friichte (Bot. Zeit. 1870, p. 281). 

 1 De Bary, loc. cit. 



