F UNGI. A SCOMYCE TES. 113 



recently shown to be the case with the genus Elaphomyces^ . The mycelium of this 

 Fungus is parasitic on the outer layers of the roots of pines and produces dichotomous 

 branching in them of an abnormal kind. Neither the formation of gonidia, nor the 

 germination of the ascospores have been observed. The tuber-like fructifications with 

 their asci are either attached to the mycelium by a distinct basal portion, as in Terfezia 

 and Delastria, or are enclosed in the young state by the mycelium, as in Tuber ; in the 

 mature state the mycelium has disappeared and the fructifications lie in the ground 

 detached and without their former investment, but covered by a cortical layer, the peri- 

 dium, which is usually a thick compact mass of pseudo-parenchyma. The spores which are 

 produced inside the fructification are set free by its decay. The interior is occupied by 

 winding chambers which are covered by the broad hymenial layers and separated by barren 

 portions. The spores in an ascus are not formed simultaneously but at different times 

 in a way not yet understood, and the number varies, being usually four, but often less. 

 There are intermediate forms between the Discomycetes and the Tuberaceae. 



6. There remain to be noticed certain Fungi which are classed with the Ascomycetes 

 as doubtful or very degenerate forms, in which the spores are formed in an ascus, but 

 the asci are not produced in a fructification but are free branches of the mycelium. 

 Among these are Exoascus and the Yeast-Fungi. 



Exoascus 2 . Exoascus Pruni, which occasions the malformation known as bladder- 

 plum in the fruits of Prunus domestica, P. insititia and other species, may serve as an 

 example of this genus. The mycelium consists of unbranched hyphae with transverse 

 septa, and grows from the parts round the fruit and the adjacent branches into the 

 young fruit, spreading there betv/een the cells and ultimately occupying the whole of it. 

 In consequence of this fungus-growth the fruits increase to an abnormal size ; the 

 part which usually forms the juicy flesh swells up, and the tissue inside it, where the stone 

 should be, does not develope, but in its place there is a cavity, the so-called 'pocket.' 

 At length the hyphae beneath the surface of the fruit put out branches, which grow 

 perpendicularly to the surface and raise up the cuticle. Each of these branches elongates 

 into a club-shaped tube which bursts through the cuticle, parts off a stalk-cell at its basal 

 extremity by a transverse septum, and becomes an ascus. Eight spores are formed in 

 an ascus. The spores sprout in germination, like the cells of the yeast-plant. How 

 the Fungus finds its way into healthy trees is not known. 



The YEAST-FUNGI 3 , in the narrower sense of the term, belong to the genus 

 Saccharomyces, and are distinguished by their power of exciting alcoholic fermentation 

 in saccharine fluids. Saccharomyces is a typical unicellular Fungus. Its cells are 

 roundish or ellipsoidal in form and consist of a delicate cell-wall and vacuolated 

 protoplasm. A nucleus has not been observed in them *. Their mode of multiplication 



1 The relations of this genus to the genus Tuber, and its connection with the Tuberaceae, still 

 require investigation. 



2 De Bary, Exoascus Pruni u. d. Taschen oder Narren d. Pflaumenbaume (Beitr. z. Morph. u. 

 Phys. d. Pilze, I, in Abhandl. der Senckenberg. Ges. in Frankfurt a. M., V. Bd. 1864), [also Vergl. 

 Morph. u. Biol. d. Pilze, Mycetozoen u. Bacterien, Leipzig, 1884. Fischer, Ueber die Pilzgattung 

 Ascomyces (Bot. Zeit. 1884).] 



3 Nageli includes the Schizomycetes under the terra 'Hefe' (Yeast-fungi), which applies to all organ- 

 isms which excite fermentation and putrefaction in contradistinction to inorganic ferments (see Nageli, 

 Theorie d. Gahrung., Miinchen 1879). Rees, Bot. Unters. ii. d. Alkoholgahrungspilze, Leipsic 1860. 

 The extensive literature on the subject of fermentation cannot be further noticed here, [but see De Bary, 

 Vergl. Morph. u. Biologic d. Pilze, Mycetozoen u. Bacterien, Leipzig, 1884, for an account of this subject 

 and the more important literature ; also Schutzenberger, Les fermentations, 4 th edition, Paris 1 884. Reess, 

 Ueber d.systemat.Stellungd.Hefepilze(Bot. Zeit. 1884). Hansen,Vorlauf.Mittheil.uberGahrungspilze 

 (Bot. Centralbl. XXI. 1884). Kny, Die Beziehung des lichtes z. Zelltheilung bei Saccharomyces Cere- 

 visiae (Ber. d. Deut. Bot. Ges. 1884). Grove, Synops. of the Bacteria and Yeast-Fungi (London, 1884)]. 



4 [The presence of a nucleus has been observed; see Schmitz, Ueber d. Zellkern d. Thalloph. (Nie- 

 derrh. Ges.)]. 



M 



