Fink : Composition of a Desert Lichen Flora 95 



the rocks of the gulch are nearly all on the west side or near the 

 bottom. This peculiar distribution is doubtless largely due to the 

 fact that the rock faces of the east side of the gulch receive the 

 direct rays of the afternoon sun. The lichens sent from the 

 rocks of this station are numbers 8, 10, 12, 13, 15, 16, 17, 19, 20, 

 22, 23, 26, 27, 32 and 33 of the list of species given above. The 

 lichens found on the soil of the bottom of the gulch are numbers 

 6, 7 and 31. The rocks forming the walls of the gulch are 

 basaltic. 



Station II is a mass of basaltic boulders, forming a cliff fac- 

 ing southward on the south side of Tumamoc Hill, altitude 792 

 m. The collection was made from all sides of the boulders ; and 

 Mr. Blumer reported the south faces of the boulders to be very 

 poor in lichen species and individuals, while the lichen flora is 

 best developed and most highly colored on the north faces of the 

 boulders. The lichens determined from this station are numbers 

 1, 2, 8, 10, 11, 12, 13, 16, 17, 19, 20, 21, 23, 26, 27 and 32. The 

 similarity between the lichen species of the basaltic rocks of the 

 first two stations will be apparent enough upon noting the simi- 

 larity in numbering, and especially when one takes into account 

 the genera represented by these numbers as well as the species. 

 Mr. Blumer's notes regarding station II state that a number of 

 moisture-requiring seed-plants, such as Celtis pallida, Abutilon 

 incanum, Encelia farinosa and a Eupatorium grow about the 

 rocks ; and doubtless there are moist places on the rocks where 

 numbers 1 and 2 grow. At least, the writer has found members 

 of the genus Endocarpiscum growing in moist places elsewhere. 

 The structural responses of the other lichens found in the first 

 two sections were sufficiently considered in the general and in 

 the seriatim statements of adaptations and need not be repeated. 



Station III is a very steep slope facing directly south on the 

 south side of Tumamoc Hill, altitude 823 m. The lichen habitat 

 consists of loose blocks of tuff and basalt, especially the former, 

 which have worked down from a quarry above. The habitat is 

 a very dry one, and nothing exists on the ash-dry soil except a 

 few bushes of Larrea tridentata. The lichens determined from 

 this station are numbers 8, 9, 10, 11, 12, 13 and 16. The meager- 

 ness of lichen species here is very apparent, but it is not certain 



