176 REPRODUCTION 



apogamous genera by Metzger^ and his work was confirmed and amplified 

 by Baur": certain hyphae of the gonidial zone branch out into larger asco- 

 gonial cells which increase by active intercalary growth, by division and by 

 branching, and so gradually give rise to the ascogenous hyphae and finally 

 to the asci. Baur looked on this and other similar formations as instances 

 of degeneration from the normal carpogonial type of development. Moreau* 

 (Fernand and Mme) have also examined Solorina with much the same 

 results : the paraphyses rise first from cells that have been produced by the 

 gonidial hyphae; later, ascogenous hyphae are formed and spread horizontally 

 at the base of the paraphyses, finally giving rise at their tips to the asci. 

 Metzger' had further discovered that spermogonia were absent and tricho- 

 gynes undeveloped in two very different crustaceous lichens, Acarospora 

 {Lecanord) glaucocarpa and Verrucaria calciseda, the latter a pyrenocarpous 

 species and, as the name implies, found only on limestone. 



Krabbe* had noted the absence of any fertilization process in Gyrophora 

 vellea. At a later date, Gyrophora cylindrica was made the subject of exact 

 research by Lindau'. In that species the spermogonia (or pycnidia) are 

 situated on the outer edge of the thallus lobes; a few millimetres nearer the 

 centre appear the primordia of the apothecia, at first without any external 

 indication of their presence. The initial coil which arises on the lower side 

 of the gonidial zone consists of thickly wefted hyphae with short cells, slightly 

 thicker than those of the thallus. It was difficult to establish their connec- 

 tion with the underlying medullary hyphae since these very soon change to a 

 brown plectenchyma. From about the middle of the ascogonial coil there 

 rises a bundle of parallel stoutish hyphae which traverse the gonidial zone 

 and the cortex and slightly overtop the surface. They are genetically con- 

 nected at the base with the more or less spirally coiled hyphae, and are similar 

 to the trichogynes described in other lichens. Lindau did not find that they 

 had any sexual significance, and ascribed to them the mechanical function of 

 terebrators or borers. The correctness of his deductions has been disputed by 

 various workers: Baur'' looks on these "trichogynes" as the first paraphyses. 

 The reproductive organs in Stereocaulon were examined by G. Wolff", and 

 the ab.sence of trichogynes was proved, though spermogonia were not wanting. 

 She also failed to find any evidence of fertilization in Xanthoria parietina, 

 in which lichen the ascogenous hyphae branch out from an ascogonium that 

 does not form a trichogyne. 



Rosendahl', as already stated, could find no trichogynes in Parmelia 

 glabra. In Parmelia obscurata, on the contrary, Bitter* found that carpogonia 

 with trichogynes were abundant and spermogonia very rare. In other species 

 of the subgenus, Hypogymnia, he has pointed out that apothecia are either 



^ Metzger 1903. ^ Baur 1904. ^ Moreau 1916. * Krabbe 1882. » Lindau 1899. 



* Wolff 1905. ' Rosendahl 1907. * Bitter 1901". 



