REPRODUCTION IN DISCOLICHENS 



i6i 



the view that there had been fertilization: the cells of the trichogyne had 



lost their turgidity and at the same time the cross-walls had swollen con- 

 siderably and stood out like knots in the 



hypha (Fig. 92). The ascogonial cells had 



also increased not only in size but in number 



by intercalary division, so that the spiral 



arrangement became obscured. Ascogenous 



hyphae arose from the ascogonial cells, and 



asci cut off by a basal septum were finally 



formed from these hyphae. Lateral branches 



from below the septum also formed asci. 

 Stahl's observations were repeated and 



extended by Borzi^ on another of the Colle- 

 maceae, Colleina nigrescens. In that plant the 



foliaceous thallus is of thin texture and has 

 a distinct cellular cortex. The carpogonia 



were found at varying depths near to the cor- 

 tical region; the ascogonium, of two and a 

 half to four spirals, consisted of ten to fifteen 

 cells with very thin walls, the trichogyne of 

 five to ten cells, the terminal cell projecting 

 above the thallus. Borzi also found spermatia 

 fused with the tip-cell. 



A further important contribution was made hy Baur" in his study of 

 Collema crispum^. There occur in nature two forms of this lichen, one of 

 them crowded with apothecia and spermogonia, the other with a more 

 luxuriant thallus, but with few apothecia and no spermogonia. On the latter 

 almost sterile form Baur found in spring and again in autumn immense 

 numbers of carpogonia- — about one thousand in a medium sized thallus — 

 which nearly all gradually lost the characteristics of reproductive organs, 

 and, anastomising with other hyphae, became part of the vegetative system. 

 In a few cases in which, presumably, a spermatium had fused with a tricho- 

 gyne, very large apothecia had developed. 



As the first-mentioned form was always crowded with apothecia in every 

 stage of development, as well as with carpogonia and spermogonia, it seemed 

 natural to conclude that the difference was entirely due to the presence or 

 absence of spermatia in sufficient numbers to ensure fertilization. The 

 period during which copulation is possible passes very rapidly, though 

 subsequent development is slow, occupying about half-a-year from the time 

 of fertilization to the formation of the first ascus. 



1 Borzi 1878. 2 Baur 1898. 



' Funfstuck (1902) suggests that the lichen worked at by Baur is Collema cheileum Ach. 



Fig. 92. Collema fnicrophylliim Ach- 

 Carpogonium and trichogyne after 

 copulation x 500 (after Stahl). 



S. L. 



