i«5 



6. Verrucaria Wig. Prim. Fl. Hoi. 85. 1780. 



The representatives of this genus are unquestionably lichens ; 

 the thallus, though crustaceous, is usually well developed ; there is, 

 however, great confusion among authors as to the limitations of 

 the genus ; some include species with simple, two-celled, and many- 

 celled to multilocular spores, both colorless and colored ; such variabil- 

 ity in spore-characters associated with imperfect descriptions of the 

 thallus (algae in particular) has caused a great difficulty in attempt- 

 ing to determine supposed species of Verrucaria. In order to 

 avoid this I have included under Verrucaria all lichens having the 

 following characteristics. 



The thallus is crustaceous but shows a high degree of differenti- 

 ation, as is indicated by the hyphal structure and its relation to the 

 algae ; the hyphal tissue is semicortical in structure, consisting of 

 closely united short cells, much like those of Acarosfora ; the 

 algae are Pleurococcus vulgaris and have much the position and 

 general arrangement in the thallus that they do in Endocarpon, to 

 which genus Verrucaria is phylogenetically related. All the species 

 examined contained Pleurococcus, though according to some au- 

 thors Chroolepus umbrina is supposed to be typical of the genus. 



The apothecia are very small, almost entirely immersed in the 

 thallus and substratum ; the perithecium (hypothecium and excipular 

 margin) is quite dark in color due to a deposition of lichenic acid 

 within and upon the hyphal cell-walls ; the paraphyses are compara- 

 tively short and almost entirely gelatinized, so much so that some 

 authors have cited the absence of paraphyses as a generic character ; 

 close examination will demonstrate that this is not the case ; the 

 spore-sacs are also much gelatinized and contain eight colorless sim- 

 ple spores ; the spore-wall is thin ; the plasmic contents are granular 

 and mixed with oil globules ; the whole presents the appearance of 

 degenerative products. It is probable that these degenerative pro- 

 cesses began with the fungal ancestor and not since lichen evolution ; 

 it is, however, very likely that the symbiotic associations hasten the 

 retrogressive changes as far as the apothecia and spores are con- 

 cerned, since these are probably of little value in the processes of 

 reproduction. The process of gelatinization begins quite early in the 

 development of the apothecia and reaches its climax at an early 

 period ; as a rule spores are few in number, while the apothecia oc- 

 cur quite plentifully. 



