164 



REPRODUCTION 



b. CARPOGONIA OF NON-GELATINOUS LICHENS. The soft loose tissue 

 of the gelatinous lichens is more favourable for the minute study of apo- 

 thecial development than the closely interwoven hyphae of non-gelatinous 

 forms, but Borzi 1 had already extended the study to species of Parmelia, 

 Anaptychia, Sticta, Ricasolia and Lecanora, and in all of them he succeeded 

 in establishing the presence of ascogonia and trichogynes. After him a 

 constant succession of students have worked at the problem of reproduction 

 in lichens. 



Lindau 2 published results of the examination of a considerable series of 

 lichens. In Anaptychia (Physcia) ciliaris, Physcia stellaris, Ph. pulverulenta , 

 Ramalina fraxinea, Placodium (Lecanord) saxicolum, Lecanora subfusca and 

 Lecidea enteroleuca he demonstrated the presence of ascogonia with tricho- 

 gynes. In Parmelia tiliacea and in Xanthoria parietina he found ascogonia 

 but failed to see trichogynes. In none of the species examined by him did 

 he observe any fusion between the trichogyne and a spermatium. 



In Anaptychia ciliaris he was able to pick out extremely early stages by 

 staining with a solution of chlor-zinc-iodine. Maule 8 applied the same test 

 to Physcia pulverulenta, but found that to be successful the reaction required 



some time. Certain cells of the hyphae mostly 

 terminal cells in the lower area of the gonidial 

 zone and even occasionally in the pith (according 

 to Lindau) coloured a deep brown, while the 

 ordinary thalline hyphae were tinted yellow. 

 He assumed that these were initial ascogonial 

 cells on account of the richer plasma contents, 

 and also because of the somewhat larger size of 

 the cells. In the same region of the thallus 

 young carpogonia were observed as outgrowths 

 from vegetative hyphae, though the trichogynes 

 had not yet reached the surface. 



At a more advanced stage the carpogonia 

 were seen to be embedded in the gonidial zone 

 and occurred in groups. The cells of the asco- 

 gonium, easily recognized by the darker stain, 

 were short and stout, measuring about 6-8 /* in 

 length and 4/4 p in width. They were arranged 

 in somewhat indistinct spirals; but the crowding 

 of the groups resulted in a confused intermingling of the various generative 

 filaments. The trichogynes composed of longer narrower cells rose above 

 the hyphae of the cortex ; they also stained a deep brown and the projecting 

 cell was always thin-walled. Lindau frequently observed spermatia very 

 1 Borzi 1878. 2 Lindau 1888. 3 Maule 1891. 



Fig. 93. Physcia pulverulenta Nyl. 

 Vertical section of thallus and 

 carpogonium before fertilization. 

 a, outer cortex; b, inner cortex; 

 c, gonidial 1 ayer; rf, medulla, 

 x ca. 540 (after Darbishire). 



