tgt1) HERRE—DESERT LICHENS 295 
is usually far more closely attached to the rocks than many of the 
species of Lecidea or Acarospora. 
In Finx’s study of the Tucson lichens, he speaks of the remark- 
able development of black lines or spots on the upper surface of 
every species having a light-colored thallus. I find practically 
nothing of the kind on the lighter-colored species at Reno, such as 
Acarospora chlorophana, Acarospora thamnina, Lecanora gibbosa, 
Buellia albo-atra, or Physcia stellaris, though all but the last named 
occur frequently where they are exposed to the full glare of a bril- 
liant sun set in a cloudless sky for ten or twelve hours daily during 
most of the year. I do find some such dark spots on Rinodina 
oreina, but not any more, if as many, as occur on it in regions 
elsewhere with a rainfall of 20 inches. Acarospora thamnina 
and other sterile light-colored lichens are often blotched with dark 
spots simulating apothecia, but a section shows them to be parasitic 
fungi. 
Certain species of Acarospora and Lecidea are noticeable for 
the thickness and comparative luxuriance of their thallus, and for 
their sterility, certain forms which I can identify with difficulty or 
not all at being persistently sterile though of a rank vegetative 
growth. 
In his study of the Tucson desert lichen flora, Frvx takes up 
the question of the amount of moisture desert rock lichens may 
obtain from the upward passage of water through the rocks. 
Geologists and botanists here in Nevada do not believe that lichens 
obtain any appreciable amount of water from the desert rocks upon 
Which they grow by the upward passage of moisture through the 
rocks. All observation goes to substantiate Frnx’s statement “that 
lichens absorb at least a large proportion of the moisture needed 
directly from water vapor of the atmosphere and from water falling 
upon them.” Incomplete experiments by me show that lichens 
hot only retain a considerable amount of moisture within their 
thalli even in the driest times, but that they imbibe moisture 
from rain with very great rapidity and in great quantity, relatively 
speaking. 
But that the desert lichens of this region do not depend upon 
water obtained by capillarity is readily understood when one exam- 
