270 DIVISION II.—COURSE OF DEVELOPMENT OF FUNGI. 
cetes. Objections to this view are drawn from the entire absence of archicarp and 
ascogonium and differentiation of ascus-apparatus and envelope-apparatus. But we 
have constantly seen variations in the amount of differentiation in these organs 
within the group of the Ascomycetes, and can therefore conceive of an extreme 
simplification; we must perhaps wait for the discovery of more thoroughly inter- 
mediate forms. 
If without waiting for more exact proof we assume a phylogenetic connection ® 
between the Exoascus-group and the Ascomycetes, two views are open to our 
adoption. Either the former group represents the simple s/arting-point of the series 
of Ascomycetes, the Saccharomycetes containing the simplest forms from which 
Ascomycetes have been gradually developed; or its members are greatly reduced 
Ascomycetes (see page 125), with extensively interrupted homology which is only 
restored with the appearance of the asci. The latter is the only admissible assump- 
tion if the account given above of the relation of the Ascomycetes to the Phycomycetes 
by affinity and descent is the true one, and it must be maintained with the necessary 
reservation so long as these relations, which are the natural conclusion from known 
facts, are not set aside by the discovery of new ones. 
Most of the species of Saccharomyces which have been mentioned above are 
the most common and practically the most important inciters of alcoholic fermentation ; 
they are the yeasts of fermentation and are for this reason generally termed Yeast- 
fungi. Some of them, beer-yeast for example, are purposely added to the liquid 
which is intended to ferment; the juices of certain fruits ferment spontaneously, the 
yeast-plants appearing in them without artificial assistance. This led the earlier 
observers to the notion, which afterwards reappeared from time to time, that the 
Yeast-fungi are formed without parentage from the organisable material contained 
in the juices of fruit. Karsten! in 1848 derived them from organised ‘vesicles,’ 
which had been normal parts of the cells of living plants and continued to vegetate inde- 
pendently after their death. But ideas of this kind have been given up for many years. 
We now know that the Yeast-fungi are derived from parent-forms as members of 
the development of a normal species of Fungus, and that their germs find their 
way from without into fermentable fluids ; this latter point will be noticed again in 
a subsequent chapter. But those who upheld this view carried on a lively controversy 
respecting the systematic or morphological relations of the Yeast-fungi, especially 
before the asci of Saccharomyces had been observed by De Seynes and Reess in 
1868 and 1870. Some writers regarded them as independent representatives of 
distinct species which always appear in the form of sprouting Fungi (Schwann, 
Pasteur, De Bary). Others, on the contrary, considered them to be special forms of 
species of Fungi which are generated in suitable fluids, and which appear in some other 
form, chiefly that of the Hyphomycetes, outside these fluids; they thought that the 
characteristic sprouting form of the plants and the yeast-fermentation depended on the 
nature of the medium, and that the Fungus could be brought back again to the other 
form, the Hyphomycetous form for example, by changing the medium. Either some 
particular species were indicated as capable of this transmutation, chiefly the common 
Moulds, species of Mucor for example, Sclerotinia Fuckeliana (Botrytis cinerea) (Bail) or 
Penicillium (Berkeley), or the capacity was supposed to exist in a great variety of Fungi, 
though here again the commonly diffused species just named stood at the head of the 
list (H. Hoffmann). ‘ 
Continued investigations have brought to light the reasons for this variety of 

' Bot. Ztg. 1848, p. 457- 
