[Vol. 2 



320 



ANNALS OF THE MISSOURI BOTANICAL GARDEN 



arisen. Further reduction of one of the gametes, or of the 

 vegetative stages, would result in apogamous forms of En- 

 domyces, the Exoaseeae, 1 the Saccharomycetes, or yeasts, etc. 

 By reduction and loss of one of the gametes without reduction 

 in size of the generalized "ascus," such forms as Ascoidea, 

 Protomyces, Taphridium, etc., may have arisen. 



Origin, progression and sterilization of the so-called tricho- 

 gyne. — There is no well developed trichogyne-like structure in 



of the known PI 



But there is evidence 



few of the forms, like certain species of 

 Cystopus, of a tendency of the oogonium, 

 probably under chemotactic stimulation and 

 a softening of the wall, to develop a short 

 process directed toward the antheridium. 

 This has been suggested by a number of stu- 

 dents (Lotsy, '07, p. 468) to be an indication 

 of the origin of the trichogyne in the As- 



comycet 



It does not mean that Cy 



2 



OTM um 



is to be regarded as an ancestral form of the 

 Ascomycetcs, though certain species do pos- 

 sess a number of peculiarities which may be 



maYic' repre^S attributed to such a hypothetical form. This 



the oogonium of some 



4sco$ 



Fig. 2. Diagram- 



ed the archicarp of 

 lichens and many 

 other Ascomycetes. 

 The fertile part is 



the ascogonium; the 

 sterile portion i s 

 the so-called "tricho- 

 gyne" ; tr.c, tricho- 

 gyne cell. 



feature of 



species of Cystopus is, however, of impor- 

 tance as it indicates one probable method 

 of origin of the trichogyne in the Ascomy- 

 cetes. The trichogyne is not a character 

 possessed by all Ascomycetes, even of those 

 which still retail) two functional gametangia. 



This, I believe, is strong evidence of the independent origin of 

 the trichogyne in the Ascomycetes. 



It arose as a copulating process or beak from the oogonium 



1 Such an origin for the Exoasceae is more comprehensible than the theory 

 that their mycelium may represent ascogenous hyphae which have migrated from 

 the condition of parasitism in the vegetative portion of a former ascocarp, to 

 parasitism on their present hosts, as suggested by Harper ('00, p. 392). 



2 One of these features is the generalized character of the sexual organs,, 

 which are polyenergid, but particularly the great variation in number of func- 

 tional egg nuclei in different species as described by Stevens ('99, '01). 



