114 FIRST GROUP. THALLOPHYTES. 



by sprouting is characteristic of the yeast-cells. Each cell in a fermentable solution 

 puts out at one or more points in its circumference a small knob-like protuberance, 

 which increases in size and by constriction and the formation of a parting wall at its 

 base is delimited from the mother-cell. Then the daughter-cell either separates at 

 once from the mother-cell or, continues united to it for some time ; if the latter happens 

 while many generations of daughter-cells are produced, the result is the formation of 

 chains of cells (sprout-chains) (Fig. 7 1 , d) . If yeast-cells are cultivated on the cut surface 

 of pieces of potato, turnip, c., single cells are converted into asci, in which from two to 

 four ascospores are formed. These can germinate at once by the production of the 

 characteristic yeast-sprouts : they can also retain the power of germination for a longer 

 time. It is only in solutions in which the fermentation is sufficiently active that the 

 yeast-cells can do without the free oxygen which is necessary for the life of other 



Fungi and of all plants ; where sugar is wanting 

 in a solution they cannot live without the access 

 of free oxygen, but they can grow in solutions which 

 do not contain oxygen provided they contain sugar. 

 Oxidation by the free oxygen of the atmosphere 

 however is favourable to their fermentive activity, 

 and the fermentive activity of a cell promotes its 

 growth under all circumstances. The yeast-like 

 sprouting which may be observed under certain 

 circumstances in some species of Mucor, as in 



FIG. 71. Saccharomycescerevisiae.a isolated cells, MtiCW raCeitlOSUS, HlUSt not mislead US intO COn- 

 b,c,d smaller and larger aggregations of sprouts, the r j ,1 r -i ,-1 n / 



cells of which multiply by sprouting. After de Bary. founding those forms With the trUC yeast-Cells of 



Magn. 390 times. t ^ e g enus Saccliaromyces ; they too have the power 



of setting up a weak alcoholic fermentation in fluids which contain sugar 1 . 



7. LICHENS. Since the researches 2 of Schwendener, with which must be 

 associated those of Bornet, Stahl and others as confirming and extending them, it can 

 no longer be doubted that the Lichens are genuine Fungi of the division of the 

 Ascomycetes with a few genera belonging to the Basidiomycetes, as Cora and 

 Rhipidonema, and that they are distinguished by a remarkable parasitism. The host- 

 plants are Algae, growing as a rule in damp situations, but belonging to a variety of 

 groups, frequently to the Chroococcaceae and Nostocaceae, still more frequently to the 

 Falmellaceae, sometimes to the Chroolepideae, rarely to the Confervaceae. The Fungi 

 which form Lichens occur only as parasites on certain species of Algae 3 , while the Algae 

 which are attacked by them, and which when united with the Fungi are called gonidia, 

 are also known in the free state and separate from the Fungi. Where the Alga which 

 is attacked by the Lichen-fungus is a filamentous Alga and the hyphal tissue is 

 developed only in small quantity, as in Ephebe and Coenogonium, the true state of the 

 case is at once apparent; and ever since Lichens of this sort have been more 

 accurately known, the suspicion has been entertained that they were in fact Algae 

 attacked by Fungi. Even before this time attention had been repeatedly called to the 

 identity of the gonidia of the Collemaceae with rows of cells of the Nostocaceae ; but in 



1 Brefeld, Untersuch. u. Alkoholgahrung in Verhandl. d. phys. Med. Ges. zu Wiirzburg, 1874. 



2 Tulasne, Memoire pour servir a 1'histoire organogr. et physiol. des Lichens (Ann. d. sc. nat. 3 

 serie, T. XVII). Schwendener, Unters. ii. d. Flechtenthallus in Nageli's Beitr. z. wiss. Bot. 1860 u. 1862 ; 

 Id., Laub- und Gallertflechten (Nageli's Beitr. z. wiss. Bot. 1868); Id., in Flora, 1872,^.11-15, and 

 Ueber d. Algentypen d. Flechtengonidien. Basel 1869. Bornet, Recherches sur les gonidies des lichens. 

 Ann. d. sc. nat. T. XVII. 1873. Stahl, Beitr. z. Kenntn. d. Flechten. Leipzig 1877 and l8 7 8 - Other 

 works are cited in the text. [See also De Bary, Morph. u. Biol. d. Pilze, &c., 1884. Marshall 

 Ward, On the structure, development and life-history of a tropical epiphyllous Lichen (Strigula 

 complanata, F.) in Trans. Linn. Soc. Lond. Bot. II. part 6. 1884. Neubner, Beitr. z.[Kenntn. d. Calicien 

 (Flora, 1883). Fiinfstuck, Beitr. z. Entwicklungeschichte der Lichenen (Jahrb. d. K. hot. Gartens z. 

 Berlin, III. 1884).] 3 See however what is said below of Arthonia. 



