DISCUSSION OF LICHEN REPRODUCTION 177 



absent or occur but seldom, while spermogonia are numerous, and he concludes 

 that the spermatia must function as spores or conidia. Baur 1 however does 

 not accept that conclusion ; he suggests as probable that the male organs 

 persist longer in a functionless condition than do the apothecia. 



Still more recently Nienburg 2 has described the ascogonium of Baeo- 

 myces sp. and also of Sphyridium byssoides (Baeomyces rufus) as reduced 

 and probably degenerate. His results dp not disprove those obtained by 

 Krabbe 3 on the same lichen (Sphyridium fungiforme). The apothecia are 

 terminal on short stalks in that species. When the stalk is about *5 mm. in 

 height, sections through the tip show numerous primordia (12 to 15) ranged 

 below the outer cortex, though only one, or at most three, develop further. 

 These ascogonial groups are connected with each other by delicate filaments, 

 and Nienburg concluded that they were secondary products from a primary 

 group lower down in the tissue. Spirals were occasionally seen in what he 

 considered to be the secondary ascogonia, but usually the fertile cells lie in 

 loose uncoiled masses; isolated hyphae were observed to travel upwards 

 from these cells, but they never emerged above the surface. 



Usnea macrocarpa if Schulte's 4 work may be accepted is also apo- 

 gamous, though in Usnea barbata Nienburg 2 found trichogynes (Fig. 95) 

 and the various developments that are taken as evidence of fertilization. 

 Wainio 5 had demonstrated emergent straight trichogynes in Usnea laevis 

 but without any sign of fertilization. 



E. DISCUSSION OF LICHEN REPRODUCTION 



In Ascolichens fertilization by the fusion of nuclei in the ascogonium 

 is still a debated question. The female organ or carpogonium, as outlined 

 above, comprises a twisted or spirally coiled multiseptate hypha, with a 

 terminal branch regarded as a trichogyne which is also multiseptate, and 

 through which the nucleus of the spermatium must travel to reach the 

 female cell. It is instructive to compare the lichen carpogonium with that of 

 other plants. 



a. THE TRICHOGYNE. In the Florideae, or red seaweeds, in which the 

 trichogyne was first described, that organ is merely a hair-like prolongation 

 of the egg-cell and acts as a receptive tube. It contains granular proto- 

 plasm but no nucleus and terminates in a shiny tip covered with mucilage. 

 The spermatium, unlike that of lichens, is a naked cell, and being non-motile 

 is conveyed by water to the tip of the trichogyne to which it adheres; the 

 intervening wall then breaks down and the male nucleus passes over. After 

 this process of fertilization a plug of mucilage cuts off the trichogyne, and 

 it withers away. 



1 Baur 1904. 2 Nienburg 1908. 3 Krabbe 1882. * Schulte 1904. 8 Wainio 1890. 

 S. L. 12 



