a so THALLOPHYTES. 
into tubes and assume hypha-like 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 Ascomycete. 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 Würz- 
burg. Yeast-cells, like all other vegetable cells, require for their growth oxygen 
either free or diff'used through the fluids 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 minute 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 Algse 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. Journ. Micr. Sc. 1875, pp. 145-149.] 
2 Reess, Botanische Untersuchungen über des Alkoholgährugspilze, Leipzig 1870. [Quart. Journ. 
Micr. Sc. 1875, PP- 142, I43-] 
^ [Comptes lendus, 1872, pp. 784-790; Quart. Journ. Micr. Sc. 1873, p. 351. — See also Mayer, 
Lehrbuch der Gahrungs Chemie, 1876; Schützenberger, Les Fermentations, 1876.] 
* Vortrag, July 26th, 1873, in the Physik.-medic. Gesellschaft of Würzburg. 
^ 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. 1864, 
and Ann. des Sei. Nat. 5^ ser, vol. VIII. 1868, as well as the French translation of this work, 
P- 352. 
