HEMIASCOMYCETES 157 



one or the other of the Endomycetaceae lines: the Schizosaccharomyce- 

 teae are connected with Endomyces Magnusii and the Saccharomyceteae 

 with E. fibuliger. The justification of this separation is uncertain, as 

 there are transitional forms between the two lines, e.g., Saccharomy codes 

 Ludwigii. 



In both lines a reduction of the thallus has arisen as a result of their 

 mode of life : in general, they form only sprout mycelium. This degenera- 

 tion of the thallus is followed by a degeneration of the sexual organs; 

 whereas the thallus is habitually altered until unrecognizable, they have 

 been able to retain traces of the form of the sexual act; gametangial 

 copulation of Eremascus has been lost but the pseudogamous substitute, 

 which has already appeared in Endomyces fibuliger, is retained unaltered 

 in the primitive Saccharomycetaceae. 



Both in the Schizosaccharomyceteae and the Saccharomyceteae, the 

 pseudogamous sexual act still is isogamous. While the former rapidly 

 develop apospory, the latter undergo a peculiar development toward 

 heterogamy. They are heterogamous as regards their products while the 

 sexual act is still isogamous (no longer the copulation canal, but one of 

 the copulation cells becomes the ascus) ; then they become heterogamous 

 as regards the sexual act (larger and older or better nourished cells 

 copulate with smaller, younger or poorer cells). From this dynamic 

 heterogamy, pedogamy and adelphogamy result. Thus paedogamy, at 

 least in the Saccharomycetaceae, may be considered a sign of retrogression. 



Hand in hand with these morphological and dynamic changes, goes a 

 weakening of the sexual act. The forms develop increasingly asexually 

 and the sexual act is completed in a smaller per cent of individuals. Also 

 the sexual act becomes more labile in this relation. It can occur earlier 

 and take place between two spores in an ascus. But it appears to be 

 completed with difficulty because of a lessening sexual power; copulation 

 tubes may still be formed, but they grow by, for they are no longer 

 attracted to, each other. Finally, the sexual act may be wholly suppressed 

 and the forms develop apomictically, which brings us to the same stage 

 reached in the Endomycetaceae by Endomyces decipiens and E. capsularis. 



In the scheme on page 156, sexual act and sexuality have changed in 

 form, place, time and content between the stages of Eremascus fertilis and 

 Saccharomyces cerevisiae. In form, it develops from gametangial copula- 

 tion to pseudogamy which becomes paedogamy, either of a parthenoge- 

 netic or an apogamous type. In place, the sexual act occurs normally in 

 the thallus, then in the gonotoconts, the asci. At first it normally closes 

 the vegetative period, while later it begins it. In content, the sexual act 

 is first a copulation of the principal fruit form, the asci, later this becomes 

 unnecessary and disappears. 



If this concept is correct, then Saccharomycodes Ludwigii cannot be, 

 as some authors (e.g., Nadson, 1911) have assumed, a primitive form, but 



