210 PLITT AND PEssIN: ON DISTRIBUTION OF LICHENS 
6. Marked illustration of restriction is shown by Leptogium 
tremelloides, Pertusaria amara, and Lobaria pulmonaria. These 
occur only in regions of low evaporation. ; 
snea and Ramalina occur only in regions where light is 
intense. The high evaporation in those regions does not seem 
to affect their distribution. 
In conclusion it may be stated that although these results 
should be regarded as preliminary ones, it is safe to say that 
this method of investigation opens up an interesting phase in 
the study of epiphytes, for in two different regions (in Missis- 
sippi and in Maine) and in two diverse types of plants (a fern 
and lichen) the investigation brings out similar results. 
The writers are indebted to Professors Duncan S. Johnson 
and Burton E. Livingston for the loan of the apparatus used. 
Thanks are especially due to Professor Ulric Dahlgren, Director 
of Harpswell Laboratory, for offering to the writers the facilities 
of the laboratory. Finally, acknowledgments should be made 
to Mr. A. F. Skutch who cared for the apparatus and made 
the records after the writers left the laboratory. 
