24 DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. _ 
LICHENS OF THE DESERT LABORATORY DOMAIN.! 
The lichens of the Laboratory domain form a remarkable assemblage 
of plants. Irom collections made by J. C. Blumer and V. M. Spalding, 
32 species have thus far been identified, but many more species are certain 
to be found when the ground is more exhaustively worked. ‘The collectors 
were asked to find any loosely foliose or fruticose lichens, and only a single 
loosely foliose species was sent and not a single fruticose one; the former, 
moreover, was possessed of very special adaptations. But very few were 
collected from the soil, although they were frequently looked for, and 
repeated requests for material from woody plants brought nothing but 
a few sterile and poorly developed specimens of a Physcia and a Placodium. 
These were collected on Parkinsonia microphylla very close to the ground, 
among rocks on a north slope. 
Of the 32 species 24 were found on rocks and, as shown by Fink (1899, 
1904), bear a striking general resemblance to those occurring in regions 
of greater rainfall on exposed granite and southward facing riprap, which 
represent xerophytic habitats. 
One may look through the whole list of 24 lichens growing on the rocks 
of Tumamoc Hill without finding more than 4 species with conspicuously 
lobed thalli. These are Placodium elegans, P. murorum, Lecanora murals, 
and Parmelia conspersa; and these when compared with lichens of the 
same species from more moist climates show, as a whole, a perceptible 
shortening of the lobes of the thalli. This condition of affairs may stand 
in relation to the dry air of the desert, or possibly to the high winds which 
prevail there. It is well known that the more a thallus is branched or 
lobed, the more young, tender, growing points are exposed, and the 
greater the amount of transpiration of moisture. It is also true that 
many fruticose lichens, certain Evernias, for example, notably lacking 
on Tumamoc Hill, can scarcely maintain themselves in open places, 
where they are subjected to strong gales, but seek protected habitats, 
where they will not be torn from their substrata. These forms, moreover, 
are usually conspicuously branched and present much surface and many 
tender, growing areas to the drying effects of wind and a dry atmosphere. 
The general form, therefore, of the rock-inhabiting lichens of the Labora- 
tory domain is advantageous from either of these points of view. 
In general, the 24 lichens collected on the rocks of Tumamoc Hill are 
protected by some sort of mechanical device, usually a definite pseudo- 
parenchymatous cortex, and inclosed, dead algal cells, which protect the 
living algal cells and the fungal hyphe of the medullary layer against 
the drying effects of high winds and the direct rays of sunlight. Zukal 
(1895) has observed that the cortex is thicker in certain lichens growing 
in places where they are exposed more than usual to intense light and 
dry atmosphere than in the same species in less-exposed positions. One 
of the most helpful studies in connection with the present problem would 
be the comparison of some of the lichens of Tumamoc Hill with repre- 
sentatives of the same species from regions having average conditions 
of light, moisture, temperature, and wind, with reference to develop- 
ment of cortex. 
_ There should also be a more thorough study of the presence and func- 
tions of coloring-matter in the cortex than has vet been made. Of the 

* Abstract from paper prepared by request and contributed by Bruce Fink, Ph. D., 
Professor of Botany in Miami University. 
