1913] REED & COOLEY—TRANSPIRATION 429 
open, although the thickened cushions are abundant. The second 
period, from July 17 to 31, marks a time in which the fungus has 
reached maturity and the leaf of the host begins to exhibit indica- 
tions of serious injury. The diseased leaves at this time, owing to 
the expansion of the ventral surfaces by the cluster cups, are 
rolled toward the dorsal surface. During this second period many 
peridia open for the liberation of aecidiospores. The third period 
studied, August 15 to 23, covers a time in which the full effects of 
the fungus upon its host were very manifest. At that time many 
of the infected leaves had fallen from the trees, or, if they remained, 
they had a greater or less proportion of dead tissue. In table III 
the percentages of water transpired in these three periods are given. 
TABLE III 
TRANSPIRATION BY PERIODS 
Percentage of water transpired by diseased leaves 
Dates York Imperial Ben Davis 
July S66 04.7 69.1 
ie Ay ei names 66.5 75:3 
vige Cries 70.7 83.4 
ol S| SS 78.3 72.4 
From these figures it appears that in the first period the average 
unit transpiration of the diseased York leaves was nearly as great 
as that of the healthy leaves. In the second period the ratio 
dropped to 66.5, and rose to 70.7 in the third period. The ratios 
in the case of the Ben Davis leaves did not materially vary from 
the first to the second periods, but they showed considerable rise 
in the third period. 
The rusted Ben Davis leaves used in the experiments had an 
average of 7.7 infections per sq. cm.; the York leaves had an 
average of 5.7 per Sq. cm. 
Part of the improvement in unit transpiration observed in 
August is no doubt due to the fact that the most seriously infected 
leaves (comparable to those used in the foregoing periods) had 
fallen off, and less seriously infected leaves were used as test objects. 
Attention may also be directed to the problem of diminished 
unit transpiration of these diseased leaves and its causes. The 
