DISCUSSION OF LICHEN REPRODUCTION 179 



the characters of male cells, i.e. very little cytoplasm and a comparatively large 

 nucleus that occupies most of the cell cavity, along with complete incapacity 

 to germinate. Brooks^ found in Gnomonia that tufts of the so-called tricho- 

 gynes originated near the ascogonial cells, but they were " mere continuations 

 of ordinary vegetative hyphae belonging to the coil." They are septate and 

 reach the surface, and the tip-cell is longer than the others as in the lichen 

 trichogyne. 



A somewhat similar arrangement is present in Polystigma, in which 

 Blackman and Welsford'^ have proved that the filaments, considered as tri- 

 chogynes by previous workers, are merely vegetative hyphae. A trichogyne- 

 like structure is also present in Capnodium, one of the more primitive Pyreno- 

 mycetes, but it has no sexual significance. 



Lindau' in his paper on Gyrophora suggested that the trichogyne in 

 lichens acted as a " terebrator " or boring apparatus, of service to the deeply 

 immersed carpogonium in enabling it to reach the surface. Van Tieghem^ 

 explained its presence on physiological grounds as necessary for respiration, 

 a view also favoured by Zukal'', while Wainio" and Steiner' see in it only an 

 "end-hypha," the vigorous growth of which is due to its connection with 

 the well-nourished cells of the ascogonium. 



Lindau's view has been rejected by succeeding writers: as has been 

 already stated, it is the paraphyses that usually open the way outward for 

 the apothecium. Van Tieghem's theory has been considered more worthy 

 of attention and both Dawson and Brooks incline to think that the projecting 

 filaments described above may perform some service in respiration, even 

 though primarily they may have functioned as sexual receptive organs. 



There is very little support to be drawn from fungi for the theory that 

 the presence of a trichogyne necessarily entails fertilization by spermatia. 

 Lichens in this connection must be judged as a class apart. 



It has perhaps been too lightly assumed that the trfchogyne in lichens 

 indicates some relationship with the Florideae*. Such a view might be possible 

 if we could regard lichens and Florideae as derived from some common 

 remote ancestor, though even then the difference in spore production — in 

 one case exogenous, and in the other in asci and therefore endogenous — 

 would be a strong argument against their affinity. But all the evidence goes 

 to prove that lichens are late derivatives of fungi and have originated from 

 them at different points. Fungi are interposed between lichens and any 

 other ancestors, and inherited characters must have been transmitted through 

 them. F. Bachmann's suggestion" that Collema pulposum should be regarded 

 " as a link between aquatic red algae and terrestrial ascomycetes such as 

 Pyronema and the mildews " cannot therefore be accepted. It seems more 



' Brooks 1910. 2 Blackman and Welsford igi'Z. ^ Lindau 1899. '' Van Tieghem 1 89 1 . 

 * Zukal 1895. ^ Wainio 1890. ' Steiner igoi. * See also Chap. VII. ' F. Bachmann 1913. 



