1915] 



ATKINSON — PHYLOGENY IN THE ASCOMYCETES 



361 



the zygote is the outgrowth from the fusion point of two equal 

 gametangia. 



Brefeld ('89, '91) also derived the Ascomycetes from the 



Phycomycetes but interpreted the ascus as the phyletic hom- 

 ologue of the sporangium, the ascus representing a special- 

 ized structure derived from the generalized sporangium in one 

 direction, while the conidia were regarded as reduced one- 

 spored sporangia. But the nuclear fusion and reduction 

 phenomena in the ascus are so fundamentally different from 

 any known cytological processes in the sporangium, that its 

 phyletic relation to the sporangium is doubtful. 1 The con- 

 jugation of the gametangia he interpreted as ordinary fusion 

 of hyphae which occurs in numerous instances devoid of all 



sexual 



significance. 



Protomyces, Ascoidea and Thelebolus, 

 with numerous spores in the ascus, were interpreted as rep- 

 resenting an intermediate condition between the generalized 

 sporangium of the Mucorales and the specialized ascus. In 

 Thelebolus it has been found that the development of the ascus 

 follows the type with crozier formation and that it is closely 

 related to Ascobolus and Rhyparobius (see Ramlow, '06; 

 Dangeard, '07). As for Protomyces and Ascoidea they prob- 

 ably represent forms with reduced sexuality while retaining 

 the ancestral character of many divisions of nuclei to form 

 numerous spores. 



Zukal ('89), influenced by Brefeld, derived the hymenial 

 Ascomycetes (like Ascobolus, Pezizales, etc.) through Thele- 

 bolus and Monascus; the stromatic Ascomycetes (whether 

 Pyrenomy cetes or Discomycetes) from the Uredinales; the 

 Gymnoascales and others with asci arising directly from the 

 mycelium, from another ancestral type. 



Lotsy ( '07, p. 469) sees no difficulty in deriving the polyener- 

 gid forms like Pyronema from the Phycomycetes. The forms 

 with spermatia, which are usually monoenergid, it would seem 

 rational, he thinks, to derive from the red algae, and this 

 raises the question as to whether the Ascomycetes are of poly- 

 phyletic (or biphyletic) origin. The great uniformity of the 



x The nuclear phenomena in the "germ" sporangium (from the zygote) are 

 not known. 



