204 +PLITT AND PEsSIN: ON DISTRIBUTION OF LICHENS 
in the morning, and two and four in the afternoon by means of 
a ‘Wynne Photographic Exposure Meter.’’ The observations 
began July roth, 1923, and ended August 23d of the same year. 
Thus, records were obtained during forty-three consecutive days. 
The different species of lichens are indicated in ‘Table I” 
together with the evaporation and the light measurements ob- 
tained for the different stations in each zone. It will be noted 
that the stations in the table are arranged according to the 
evaporation rates for each station. 
It is realized that the ectinometer is not especially suitable 
for measuring the light intensity, since the rays that act on the 
photographic paper are not the ones that affect the main activi- 
ties of the plant. It may be sufficiently accurate for our purpose 
since it gives the comparative light intensity of two regions for 
the kind of light it records. The readings obtained by means 
of this instrument were compared with those obtained in direct 
sunlight. It was found that it took four seconds (the average 
of four tests) to change the color of the photographic paper, 
when the ectinometer was exposed four times at noon to direct 
sunlight. Four seconds were then regarded as the standard or 
maximum light intensity. All the other readings obtained were 
computed as percentage of the intensity of the light in the open. 
TABLE I 
RELATION OF EVAPORATION AND LIGHT TO THE DISTRIBUTION oF LICHENS 
N THE TRUNK OF QUERCUS RUBRA 
Station Exposure Lichen Evaporation Light 
Ito2m.from Northwest Conotrema urceolata 427.62c.c. 6.2% 
ground Pertusaria multipuncta’ in 43 days 
I 
1to2m.from South Buellia parasema 432-13 ce.. 13.8% 
ground Lecanora albella in 43 days 
Lecidea vernalis 
—— a 
II Loba — 
Paris a sp 
Pertusaria amara 
