99 



4. Stictidaceae. Just how extensively this group of fungi is rep- 

 resented among the lichens is impossible to determine. Very likely 

 Thelotrema^ Urecolaria and Gyalecta find their fungal ancestors here, 

 but further investigation is necessary to demonstrate the correctness 

 of this supposition. 



5. The Sphaeriaceae. The fungal ancestors of the Verrucari- 

 aceae are doubtless derived from the Sphaeriaceae. Whether Endo- 

 carpon is represented by the same fungal ancestor as Verrucaria or 

 not, will perhaps always remain undecided, but the probabilities are 

 that such is the case. The apothecial and spore characters are es- 

 sentially the same in both genera. The Sphaeriaceae form a group 

 of the Pyrenomycetes as contrasted with the other families which be- 

 long to the Discomycetes. 



III. THE ALGAL TYPES. 



Concerning the algal ancestors of lichens, there is comparatively 

 little difficulty to be encountered, for in the majority of species the 

 life-history of the algal symbiont is known. We will consider only 

 the forms of algae occurring in the Ascolichenes. 



There is considerable confusion caused in the study of the lichen- 

 algae by the fact that a given lichen-species is not absolutely limited 

 to one and the same algal form. This is evident from the vary- 

 ing reports of lichenologists ; for example, one author gives Gloe- 

 ocapsa as the symbiotic alga of Li china conjinis, another gives 

 Polycoccus punctiformis, a third gives both forms as occurring in 

 this lichen. The latter author is perhaps right ; that is, both species 

 of algae occur in the same thallus. It may, however, be probable 

 that one alga predominates, or even wholly supplants the other; in 

 the specimens which came under my observation Gloeocapsa pre- 

 dominated. Cystococcus humicola is said to be the symbiotic alga of 

 Baeomyces roscus, but I have found that Gloeocapsa polydcrmatica 

 is also present. Some lichens have two forms of algae quite con- 

 stantly present, as, for example, Solorina crocca. In spite of the 

 variation and exceptions mentioned, the rule is that a given lichen 

 contains only one species of alga and this is constantly present. We 

 shall now briefly discuss the algal species which enter into the for- 

 mation of the Ascolichenes. 



i. Cystococcus humicola. This species occurs in the majority 

 of lichens ( P/iyscia, Parmelia, Usnca, Bryopogon, Cladom'a, 



