274 PHYLOGENY 



In fungi there is also a structure considered as a trichogyne^ which, in 

 the Laboulbeniales, is a free, simple or branching organ. There is no other 

 instance of any similar emergent cell or cells connected with the ascogonium 

 of the Ascomycetes, though the term has been applied in these fungi to 

 certain short hyphal branches from the ascogonium which remain embedded 

 in the tissue. In the Ascomycetes examined all traces of emergent receptive 

 organs, if they ever existed, have now disappeared; in some few there are 

 possible internal survivals which never reach the surface. 



In Ascolichens, on the contrary, the " trichogyne," a septate hyphal 

 branch extending upwards from the ascogonium, and generally reaching the 

 open, has been demonstrated in all the different groups except, as yet, in 

 the Coniocarpineae which have not been investigated. Its presence is a 

 strong point in the argument of those who believe in the Floridean ancestry 

 of the Ascomycetes. It should be clearly borne in mind that Ascolichens 

 are evolved from the Ascomycetes: these latter stand between them and 

 any more remote ancestry. 



In the Ascomycetes, there is a recognized progression of development 

 in the form of the sporophore from the closed perithecium of the Pyreno- 

 mycetes and possibly through the Hysteriaceae, which are partially closed, 

 to the open ascocarp of the Discomycetes. If the fungal and lichenoid 

 " trichogyne " is homologous with the carpogonial organ in the Florideae, 

 then it must have been retained in all the groups of Ascomycetes as an 

 emergent structure, and as such passed on from them to their lichen 

 derivatives. Has that organ then disappeared from fungi since symbiosis 

 began ? There is no trace of it now, except as already stated in Laboul- 

 beniales with which lichens are unconnected. 



Were Ascolichens monophyletic in origin, one could more easily suppose 

 that both the fungal and lichen series might have started at some early stage 

 from a common fungal ancestor possessing a well-developed trichogyne 

 which has persisted in lichens, but has been reduced to insignificance in 

 fungi, while fruit development proceeded on parallel lines in both. There is 

 no evidence that such progression has taken place among lichens ; the theory 

 of a polyphyletic origin for the different series seems to be unassailable. At 

 the same time, there is no evidence to show in which series symbiosis started 

 first. 



It is more reasonable to accept the polyphyletic origin, as outlined above, 

 from forms that had already lost the trichogyne, if they ever really possessed 

 it, and to regard the lichen trichogyne as a new organ developing in lichens 

 in response to some requirement of the deep-seated ascogonium. Its sexual 

 function still awaits satisfactory proof, and it is wiser to withhold judgment 

 as to the service it renders to the developing fruit. 



^ See p. ilT et seq. 



