Vol. I] STEWART— LICHENS OF GALAPAGOS ISLANDS 435 



ing to branches, dead sticks, grass culms, etc. Two species 

 which occur mostly in the dry regions are Physcia picta and 

 Lecanora punicea, both of which are found largely on the 

 branches of Bursera graveolens, although the first is also one 

 of the common forms inhabiting lava-boulders in the dry 

 regions. Foliose lichens are neither as abundant as a whole, 

 nor do they lend as striking an aspect to the vegetation in 

 the places where they occur, as do the fruticose forms. 



Of the rock-inhabiting forms, Placodium murorum and 

 Physcia picta seem to be the most common. They often cover 

 the lava-boulders on the lower parts of the islands to such an 

 extent as to give them, when seen from a short distance, the 

 appearance of being covered with paint. Rock-encrusting 

 forms are seldom found on lava of recent origin, but rather 

 where oxidation has set in, and at least the surface of the lava 

 has begun to disintegrate. They are seldom found in the 

 moist regions, even where there are exposures of lava which 

 apparently would furnish them with a suitable habitat. Two 

 forms which encrust the branches of trees are Verrucaria 

 ocraceo-flava and Pyrenula aurantica, both of which are 

 found in the dry regions. 



From the above it is seen that lichens are common through- 

 out the dry and the transition regions, but decrease in numbers 

 in the moist regions. The transition is distinctly the region 

 for Hchens, probably because there is more moisture in this 

 region than lower down; but why they are not more abundant 

 in the moist regions where there is a still greater amount of 

 moisture, I am unable to say. In the moist regions, in so far as 

 the epiphytic forms are concerned, their place seems to be taken 

 by the leafy hepatics, which often cover the trees and bushes 

 in great profusion. Foliose and fruticose forms present the 

 greatest display where there is at least a fair amount of 

 moisture, while the encrusting forms seem to have a distinct 

 preference for the dryer parts of the islands. 



Alectoria Ach. 



A. sarmentosa Ach. — Abingdon Isl. : very abundant on 

 the branches of small trees and bushes at 500-900 ft. (No. 

 415). Albemarle Isl. : Cowley Bay, common on the branches 



