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 1 . 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 2 . 



Section LXXVIII. 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 Exoaseus-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- 



1 Ann. d. sc. nat. ser. 6, IV, p. 9. 



2 Traite de Botanique. 



