34 BOTANICAL GAZETTE [JANUARY 
record of station 1B (18.6 cc.) and of station 1 (19.5 cc.), a differ- 
ence of only 0.9 cc. (4.3 per cent) would seem to indicate that the 
canopy exercises only a slight effect in reducing evaporation from 
the herbaceous layer. ‘‘On the basis of these results it would 
appear entirely unwarranted to assign evaporation as a causal 
factor in succession.” 
Licut.—tThe light determinations were made with a Waynne’s 
Infallible Meter, as this was the only device available. All read- 
ings seek to represent the maximum shade conditions due to the 
canopy; all part shadows due to the trunks were avoided. The 
TABLE III 
AVERAGE DAILY EVAPORATION IN CC., AUGUST 4-31, 1918 
5 Pee EE Lower Pines, B. I TSO Saag ae 
5 | SO es Lower Pine I Bos ea Ao 
Be eas Lower Pines Terrace 2 TO:4 a ee, eae 
Oc ae ey Upper Pines, 4 To 8 eee 
p SU kenga Upper Pines, S 2 Si i Nee 
ee en ste Upper Pines, E. T. 2 Moe hee 
rere alien Upper Pines, E. C. 2 16.8 12.79 
| one Jack pine 2 ga oly Oe Ree mine a Ss 
Ce eels: Black-white oak 2 BG os aa eee ee 
ee earner Open-standard I 6S Leese 
8 SO ae a ars Garden, Kalamazoo I Re: ee ae Seamer 
meter was placed upon the ground and the stopwatch held behind 
the back; both were released simultaneously. When the solio 
paper merged imperceptibly into the darker standard, the watch 
was stopped and the reading recorded. The results represent the 
averages of eight or ten readings (table IV). All light data are 
referred to full sunlight, which for convenience of comparison are 
reduced to the standard one, and all habitat records are correspond- 
ingly reduced to the same standard and expressed in the form of 
a ratio. Thus in station 1 the canopy reduces the sunlight to 
one-fifteenth its full intensity. 
The range in the light ratios is largely a question of density of 
stand and so density of canopy. It is interesting to note that the 
yellow pine canopy with the same density of individuals produces 
a light screen of only about one-half the value of that of the white 
