94 



Mycologia 



area, in spite of its special protective devices. Species of Aca- 

 rospora, on the other hand, form a large proportion of the list 

 of twenty-five lichens of the rocks and are more often seen 

 on rocks closely examined than those of any other genus. Per- 

 haps Acarospora xanthophana is the most common lichen in the 

 area studied, though the less conspicuously colored Acarospora 

 Carnegiei may prove more common on close examination in the 

 region. Lecanora has either an upper cellular cortex or a pseu- 

 docortex of entangled hyphae, and Plac odium shows a similar 

 structure. The one Parmelia is a very closely adnate species, 

 which the writer has observed to possess a stronger cortex than 

 the closely related Parmelia caperata, which usually grows in 

 less xerophytic conditions. Buellia shows the special responses 

 to need of protection in the well-developed exciples, hypothecia 

 and paraphyses, which make its existence possible in the dry 

 environment, while Biatora, closely related but less favored in 

 these three respects, is entirely absent or so rare as to be entirely 

 overlooked in collecting. Buellia has no cellular cortex above, 

 and the algal cells and the surrounding fungal hyphae are pro- 

 tected above only by a thin pseudocortex of entangled hyphae. 

 Dermatocarpon is well protected by strong cortices; and Der- 

 matocarpon miniatum, the only species not closely adnate, is 

 attached to the rocks by a very strong umbilicus, while the lower 

 cortex is so strongly developed that no ordinary wind can tear 

 the plants from the rocks. This plant is also able to maintain 

 itself more effectively because tough and elastic like rubber when 

 wet, so that, though pliable before the wind in this condition, 

 it is scarcely more likely to be torn loose when wet than when 

 dry. Pyrenopsis, Endocarpon, and the two species of Verru- 

 caria were rarely seen in the collections and need not be con- 

 sidered important floral elements. 



The Stations 



The lichens sent for study were collected from seven stations. 

 Station I is the bottom of the gulch a short distance west of 

 the Desert Laboratory, altitude 762 m. The gulch runs north- 

 west, and the lichens of the rocks were collected from rocks 

 facing northward on the west side of the gulch. The lichens of 



