88 
Table VIII. — Maximum and minimum temperatures with direction and velocity of wind, 
and character of the day, Dodge City, Kans.,from Mar. 20 to May SI, 1907 — Contd. 
Date 
(1907). 
May 
Apr. 27 
2S 
29 
30 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
13 
14 
Weather. 
Direc- 
,Maxi- Mini- ■ tion 
mum. mum. j of 
'wind. 
Clear 
Fair 
Cloudy... 
Fair 
....do... 
Cloudv... 
Fair..'.... 
....do.... 
Cloudv... 
....do.... 
....do.... 
Fair 
Clear 
....do.... 
....do.... 
....do.... 
Fair 
Clear 
°F. 
°F. 
81 
37 
59 
32 
42 
25 
45 
20 
62 
37 
67 
32 
33 
27 
57 
27 
43 
41 
50 
42 
60 
40 
68 
43 
71 
49 
78 
45 
S4 
48 
90 
60 
70 
39 
55 
34 
N. 
N. 
N. 
NW. 
SE. 
NW. 
NW. 
SE. 
SE. 
XE. 
E. 
N. 
E. 
NW. 
SE. 
SE. 
NW. 
xw. 
Ye 
locity 
of 
wind. 
Miles 
per 
nour. 
16 
16 
18 
7 
12 
18 
20 
22 
Date 
(1907). 
Mav 15 
16 
17 
18 
19 
20 
21 
22 
23 
24 
25 
26 
27 
28 
29 
30 
31 
Direc- Ye- 
Weathpr Maxi- Mini- tion ioeity 
ier - mum. mum. of of 
wind. wind. 
Clear.... 
do... 
Fair 
Cloudy.. 
Clear.... 
Fair 
....do... 
Clear.... 
Fair 
....do... 
Clear. . . . 
.....do... 
do... 
Cloudv.. 
do... 
do... 
Fair 
F. 
°F. 
67 
30 
W. 
86 
42 
SE. 
92 
53 
SE. 
81 
00 
NE. 
73 
50 
N. 
81 
50 
SE. 
8fi 
60 
SE. 
88 
65 
SE. 
87 
64 
SE. 
78 
00 
SE. 
74 
47 
W. 
62 
37 
NW. 
64 
30 
SE. 
52 
42 
SE. 
58 
46 
SE. 
59 
49 
N. 
67 
43 
NW. 
Miles 
per 
hour. 
10 
17 
13 
10 
24 
35 
33 
32 
29 
41 
So 
16 
28 
22 
11 
24 
INFLUENCE OF TEMPERATURE ON DIFFUSION. 
Directly and indirectly, temperature is responsible for the destruc- 
tive abundance of Toxoptera graminum in the United States. Di- 
rectly, because the species will breed throughout the winter months 
at a temperature under which its natural enemies will remain inac- 
tive, and besides, it is probably due to this influence that the sexual 
forms and eggs occur, so far as known, only over the northern por- 
tion of its range. Our extended investigations have led to the sus- 
picion that, but for the viviparous reproduction in such overwhelm- 
ing numbers in the South, during winter end early spring, to drift 
northward with the season, there would be little if any damage caused 
by its occurrence in the Xorthern States, where in fairly severe win- 
ters it probably winters over in the egg stage only. For this 
reason the authors have thought investigations of the egg and its 
development of decided economic as well as scientific importance, 
and the junior author has therefore made a brief study of the em- 
bryology of the species. 
The temperatures prevailing over the country where Toxoptera 
has worked its most serious ravages, and departures from the normal 
during the season of greatest activity are all given on the tempera- 
ture diagrams, Xos. I to V (pp. 15, 21, 25, 26, 28) . The upper numbers 
indicate the normal temperature, the lower the departure therefrom 
(" + " meaning above and " — " below). Each separate page relates 
to one of each of the five consecutive outbreaks. From these it will 
be seen that outbreaks of Toxoptera have succeeded only winters with 
