♦250 THA LL OPHVTES. 



into tubes and assume hypha-likc forms, as asserted by Cienkowski ', appears to be 

 uncertain. Reess^, however, has discovered that when yeast-cells are grown on the 

 surface of cut pieces of potato, turnips, &c., they attain a larger size, and the pro- 

 toplasm contained in them breaks up into from two to four roundish endogenous 

 gonidia, which, when placed in a saccharine fluid, at once again produce yeast-cells 

 by budding and abstriction. Reess considers these endogonidia of Saccharomyces to be 

 ascospores, and the yeast-fungus therefore to be an Ascomycetc. Brefeld, however, 

 makes the forcible objection to this view, — that if a yeast-cell which forms gonidia is 

 considered an ascus, and the gonidia ascospores, it must be shown that the supposed 

 ascus is developed from an ascogonium, i.e. from a female sexual organ, as in the 

 Ascomycetes. Such an origin has, however, never been proved, and is extremely 

 improbable. 



The view advocated by Pasteur ^, and since his time very popular, but never enter- 

 tained by me, that the yeast-fungus can live in fluids which do not contain any oxygen 

 diffused through them, and that they obtain the oxygen necessary for their respiration 

 by the decomposition of chemical compounds, and especially by that of sugar into alcohol, 

 carbon dioxide, and other products, has been shown to be altogether without foundation 

 by the recent researches of Brefeld * carried out in the botanical institute of Wiirz- 

 burg. Yeast-cells, like all other vegetable cells, require for their growth oxygen 

 either free or diffused through the fluid ^. The Fungi of fermentation afford no 

 exception to this general law, and are only distinguished by the fact that they are 

 able to make use of even the most minyte quantities of oxygen diffused in the fluid. 

 If the saccharine fluid is altogether free from diffused oxygen and from other 

 nutrient substances, fermentation still takes place, but the yeast-cells do not grow, but 

 pass into a dormant condition, perishing after a time; dead yeast-cells do not cause 

 fermentation. It follows from this that the decomposition of the sugar into alcohol and 

 carbon dioxide is caused by the living yeast-fungus, but has nothing to do with its 

 respiration, growth, or nutrition ^\ 



CLASS II. 

 ZYGOSPORES. 



According to the principles laid down in the Introduction to the group, this 

 class comprises plants which have hitherto been placed among Algae on the one 

 hand and among Fungi on the other hand,— all those, in fact, in which sexual 



^ [Bull. Acad, imp. St. Petersb. 1872, vol. XVII ; Quart. Joum. Micr. Sc. 1875, pp. 145-149.] 



2 Reess, Botanische Untersuchungen liber des Alkoholgahrugspilze, Leipzig 1870. [Quart. Joum. 

 Micr. Sc. 1875, PP- 142, 143.] 



2 [Comptes lendus, 1872, pp. 784-790; Quart. Journ. Micr. Sc. 1873, p. 351. — See also Mayer, 

 Lebrbuch der Gahrungs Chemie, 1876; Schiitzenberger, Les Fermentations, 1876.] 



* Vortrag, July 26th, 1873, in the Physik.-medic. Gesellschaft of Wiirzburg. 



5 The nature and the necessity of respiration in plants was first pointed out by me in my 

 Handbuch der Experimental-physiologic, pp. 263-264; (see infra. Book III. Chap. 2. Sect. 6). 



^ On other Fermentation-fungi see Van Tieghem, Ann. Scientif. de I'ecole normale, vol. I. 1S64, 

 and Ann. des Sci. Nat. 5® ser. vol. VIII. 1868, as well as the French translation of this work, 

 p. 352. 



