THE FUNGI 



191 



very small number of Lichens, but are usually absent. Pycnidia, 

 or spermogonia (Fig. 155, B), like those of the Eusts, and many 

 Ascomycetes, are of common occurrence. Minute conidia are pro- 

 duced in these, and may germinate and produce a mycelium in 

 many cases. Whether these are sometimes male reproductive cells 

 is still somewhat doubtful. 



With the exception of two genera of tropical Lichens (Cora and 

 Corella) , which produce, basidiospores, the characteristic spores are 

 ascospores, which are borne in fructifications very much like those 

 of the typical Ascomycetes. The ascospores are usually eight in 

 number, and may be either unicellular or multicellular (Fig. 155, C). 



B 



FIG. 155. A, Collema microphylla, showing ascogenous hypha, with trichogyne, t. 

 (After STAHL.) B, spermogonium of Collema sp. (X 45). C, Sticta puhnonacea, 

 asci and paraphyses (X250). D, crustaceous Lichen (Graphis) growing on the 

 bark of a Beech ; ap, apothecia (X 3). 



The type of the fruit is either open (Apothecium), like that of the 

 Cup-fungi, or closed (Perithecium), like that of the Pyrenomycetes. 

 In the Collemaceee, a family of simple gelatinous Lichens, the 

 formation of the apothecium is preceded by a specially modified, 

 enlarged hypha, whose extremity forms a slender projecting struc- 

 ture, which has been compared to the trichogyne of the Red Algae 

 (Fig. 155, A). According to Stahl, this is fertilized by means of 

 spermatia derived from the spermogonium. The question of actual 

 fertilization has, however, been disputed. From this ascogonium 

 the apothecium, or at least the ascogenous portion, is developed, 

 much as in such a Cup-fungus as Pyronema. In most of the 



