May, 1922] TRELEASE INCIPIENT DRYING AND WILTING 
sine in question. Considering the half-angle as A (the angular divergence 
of one pinna wing from its vertical or central position, this being one half 
of the angle of divergence between the two wings), the relation between 
foliar water content and the magnitude of angle A is shown by the following 
general equation of proportionality: 
y = M sine A -\- L, 
in which y and L have the meanings given above and ikf is a new slope 
constant. The values of M for the five tests with excised pinna samples 
are shown below: 
Test I Test 2 Test 3 Test 4 Test 5 
I.IO4I 0.9775 0.8961 1.0786 0-5704 
Generalizing in a very rough way, it may be said that M is about unity, 
and that the water content of these leaves (in grams per loo sq. cm. of 
area, one side) is numerically about equal to the sine of the angle of single- 
wing divergence plus 2. 
Pinnae still attached. Opportunity was not presented for the testing 
of the quantitative relations between foliar water content and position of 
the pinna wings with pinnae still attached to trees in the open. As table 
2 shows, the records of hourly changes in apparent pinna width throughout 
the day are useful in forming a picture of the diurnal march of these changes 
and, presumably, of the turgor fluctuations in the hinge cells, upon which 
the position of the pinna wings depends. The maximum distance between 
the edges of the pinna occurred, on each day except May 2, at 6 a.m., the 
time of the earliest test, thus indicating that the hinge cells were more 
completely saturated with water at this hour than at any other hour at 
which tests were made. The occurrence of the maximum at 8 a.m. on 
May 2 is probably related to a fall of rain that occurred betw^een 7 and 8 
o'clock on that day. By 7 a.m. on most days the pinna wings had already 
begun to droop, and the angle of divergence continued to decrease, hour by 
hour, reaching a minimum value at some time between 11 a.m. and 5 p.m., 
the minimum width usually occurring between i p.m. and 3. If Copeland's 
(2) interpretation of this phenomenon and the indications suggested by the 
present tests with excised pinnae represent what happens, it may be sup- 
posed that the greatest incipient drying occurred usually between i p.m. 
and 3. After reaching the minimum the pinnae began slowly to open, and 
. by 6 p.m. they had usually expanded to about the condition shown for 
7 a.m. or 8. Since other tests, continued throughout the night, showed 
that the maximum apparent width was reached some time early in the 
morning, and that it had begun to decrease somewhat by 6 a.m., when the 
tests here reported were begun, it is suggested that the maximum water 
content of the hinge cells probably usually occurs during the hours of dark- 
ness, very early in the morning. The observed fact that the growth rate 
