362 BOTANICAL GAZETTE [NOVEMBER 
observe no influence produced by differences of temperature other 
than that of acceleration or retardation, but as conditions of nutrition 
are greatly affected by temperature, it is conceivable that it may be 
in some cases an important factor in determining variability. On 
these considerations I have sought to compare the season of 1903 
with that of 1900 with respect to temperature, precipitation, and 
light. As the U. S. Weather Bureau records are not complete for 
any of these factors at Clifton, I have compared the conditions at 
the nearest stations at which complete records were available. In 
fig. 18 these comparisons are represented graphically, the temperature- 
curves representing conditions at Dayton, Ohio, about 60 km distant, 
the precipitation-curves made from data for Cedarville, Ohio, 10 v 
distant, and the curves for light-intensity from the self-recording 
instrument at Cincinnati, Ohio, 160*™ distant. These data are 
tabulated in Tables I, K, and L, along with the eleven-year OF 
twelve-year normal, and such fragmentary data as were attainable 
for Clifton itself. 
As this is the first attempt to refer changes in the variability of 
plants in a state of nature to definite climatic changes, there are 
obvious difficulties in the way of making satisfactory interpretations, 
and these difficulties can be overcome only by further study. id 
need to know (a) the relative importance of the several factors involved, 
(b) the harmonic optimum of each climatic factor for the species in 
question, (c) whether the critical period is that which precedes oF 
that which accompanies differentiation, (d) the time of beginning 
and ending of the period of differentiation. 
TABLE I. 
TEMPERATURE IN DEGREES CENTIGRADE. 
, 0. 
Dayton, O. srseeis 
3 
1900 1903 r1-yr. normal] —_ 790° 109 
8.9 
BEM oS eset ei ue 2.0 + 3 4-3 rates 10.6 
PRE ros os aaa 11.3 10.7 II.3 ae 17-9 
MME aS dicigigowh eared 18.4 18.4 ee care 17-9 
WU rare irr k ccc eees 22.4 18.9 22. eos 23-0 
Oh ore 24.7 24.0 24.8 a8 22.6 
WAMBORL Coby ore foe ek 26.2 2555 23.0 25° . 
Semember. sks ov ae 22.7 19-7 19 ue 13-1 
Seer ia cs ete 17.2 13-1 12. Se 
Oe 
E aoe 
bee 
