CHAPTER V,—COMPARATIVE REVIEW.—DOUBTFUL ASCOMYCETES. 269 
Saccharomyces ellipsoideus; it would appear to be an evident case of partial 
division or free cell-formation (see page 61), in which the observed facts perfectly 
correspond to what is known of the formation of spores in smaller asci (Exoascus, 
Eurotium). The term asci is accordingly chosen or retained. It is true that there 
are differences of opinion with regard to the process in question. Cienkowski suspects 
that in S. Mycoderma the whole of the protoplasm of the mother-cell is divided 
into spores, and Brefeld speaks in the same way as regards other species, (‘ wine-yeast’) 
in so far as he considers the sporogenous process in Saccharomyces to be like that in 
Mucor, regarding the latter indeed as a case of partial division. It is otherwise in the 
Saccharomycetes examined by Reess and myself. The continued presence of the 
parietal layer of protoplasm after the formation of the spores is decisive in their case 
even now, when the distinction between ‘free cell-formation’ and (total) division is 
less sharp than it once was. The spores are not formed in the sporangia of 
Mucor in the same way as in Saccharomyces (see page 74). Lastly, Van Tieghem 
has proposed a view which differs entirely from any other‘. He thinks that the 
spores of Saccharomyces are produced by the division of the whole of the protoplasm, 
but that they are pathological formations induced by the assaults of Bacteria ; this idea 
was suggested by the behaviour of spores of Mucor in presence of Bacteria, but it is 
at once refuted by the observation of a good specimen grown beneath the microscope 
in distilled water and free from Bacteria, and appears to have been recently abandoned 
by its author”, , 
Section LXXVII. There can be no doubt, from what we know of the history 
of development in the ascogenous Saccharomycetes, that they are immediately 
connected morphologically with the Exoasci. The differences in form between them 
and the Exoasci, whose hyphae are broken up into asci, would even allow of the 
two groups being united into one genus. The two genera therefore together form 
a natural group, which may be called here the Exoascus-group. 
If we enquire further into the connection of this group with other Fungi, we can 
only take morphological arguments into consideration in determining the question. 
No decisive argument of the kind is to be drawn from the simple vegetative structure ; 
the tendency to vegetate by sprouting or the actual occurrence of this mode of vege- 
tation in Saccharomyces cannot determine anything, for this phenomenon occurs in 
the most heterogeneous fungal groups, as has been already pointed out and will be 
again noticed below. But our group forms asci, and this peculiarity it shares only 
with the Ascomycetes, if we disregard Protomyces, which, however, is much further 
removed from it (see p. 171), and this must be decisive at present for its connection 
with the Ascomycetes. Brefeld’s early opinion, expressed in the year 1876, that 
Saccharomyces belongs to the Mucorini was disposed of when it was shown that 
the chief argument in its favour drawn from the similarity in the mode of spore- 
formation cannot be maintained. 
The connection with the Ascomycetes rests entirely on the resemblances which 
have been pointed out between the two groups. It remains uncertain how far these 
resemblances are the expression of natural and phylogenetic affinity. That they are 
the results of such an affinity is rendered highly probable by the great agreement 
between the hymenia of the more highly differentiated Exoasci and typical Ascomy- 

x 
' Ann. d. sc. nat. ser. 6, IV, p. 9. 
2 Traité de Botanique. 
