CHAPTER XI 



HEMIASCOMYCETES 



The Hemiascomycetes form the link between the Ascomycetes and 

 the Phycomycetes. According to the classification followed here they 

 fall into two orders, Endomycetales (Saccharomycetales) and Taphrinales 

 (Exoascales). The Endomycetales include those forms in which an ascus 

 arises directly as product of the sexual act (wherever this takes place). 

 They resemble the Zygomycetes, as will appear in the following discus- 

 sion, only, instead of the zygospore, an ascus develops as a hypnospore. 

 The Taphrinales include two isolated, incompletely investigated families 

 which have some primitive characters in the development of their asci, 

 without any closely related forms in the Ascomycetes known at present. 



ENDOMYCETALES 



The Endomycetales are divided into three f amilies : the Dipodascaceae, 

 the Endomycetaceae and the Saccharomycetaceae. In the Dipodas- 

 caceae, a multispored ascus arises from the copulation of coenocytic 

 gametangia. In the Endomycetaceae, the gametangia (wherever they 

 are formed) are uninucleate at the time of copulation ; each zygote devel- 

 ops to a typical ascus of eight or fewer spores. In the Saccharomyce- 

 taceae, gametangial copulation is replaced by a pseudogamy whose 

 product (if it really is completed) is a typical ascus of not more than eight 

 spores, as in the Endomycetaceae. Both the Endomycetaceae and 

 Saccharomycetaceae develop rapidly to apomictic forms. 



Dipodascaceae. — The only known representative of the family, 

 Dipodascus albidus, was originally found in the slime-flux of a bromeliad 

 in Ecuador, later in the same habitat on birch in Sweden. The hyphae 

 are branched, septate, divided into multinucleate cells of variable length. 

 In nutritive solution, they break up into oidia. Under unfavorable 

 conditions, they form gemmae: their content rounds off and surrounds 

 itself with a thick membrane. 



After a few days, two neighboring cells put forth young copulation 

 branches directly beside the septum separating them (Fig. 84, 1). At first 

 both copulation branches are of the same size and it is impossible to 

 determine which will later be the male and which the female. Frequently 

 the female branch appears somewhat earlier and survives through the 

 whole development of the male. Occasionally both copulation branches 

 may arise from different hyphae (Lagerheim, 1892; Juel, 1902; 1921; 



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