PLITT AND PESSIN: ON DISTRIBUTION OF LICHENS 209 
Physcta stellaris (L.) Nyl. 
Several specimens of this lichen were found on the tree. 
There seemed to be no definite distribution. 
Pyrenula nitida (Schrad.) Ach. 
One specimen of this lichen was found at about six meters 
from the ground on the northwest side of the tree. 
Ramalina canaliculata Fr. 
This licheri was found only in the upper half of the tree. 
At first a very few depauperate specimens were found, but at 
the upper third of the tree the lichen was very abundant. 
Possibly the patches on the lower part of the tree were washed 
down by the rains from above. 
Ramalina farinacea (L.) Ach. 
A small patch of this was found on the upper third of the tree 
on the south side. 
Usnea florida (L.) Hoffm 
The distribution of this lichen was very similar to that of 
Ramalina canalhculata. 
Usnea hirta (L.) Hoffm. — 
This lichen was found in abundance in the same regions 
on the tree inhabited by U. florida. 
Xanthoria parietina (L.) F ‘ 
One patch of this eae was found near the very top of the 
tree on the northwest side. 
SUMMARY 
1. The evaporating power of the air was found to be different 
at the different sides and heights of the tree. 
2. The evaporating power of the air seems to be the condition 
which most affects the distribution of the lichens. 
3. Certain lichens may be restricted to certain heights or 
sides of the trunk. Their restriction depends on the evaporation 
rates at those regions. 
4. Some lichens seem to have no restrictive distribution, 
and occur all along the height of the tree, on any side. 
5. Some lichens seem to show preference for the north side; 
others for the south side. 
