ss 



SPRING GRAlK-APHIS OB ' * GEEEX BUG. 





Table YIH. — M aximu m and minimum temperatures with direction and rdocity of wind, 

 and character of the day, Dodge City, Kara., from Mar. 20 to May 31, 1907 — Contd. 





"":,:-: 



-, -._ . - - 





Mree- Ve<- 

 Masl- Mini - ran fcjeity 



~-=^ — =. of of 



Apr. 27 dOK. 



2S Fii-.. 



. . ~ 17 . 



do. 



. :■ -- 



do 



do 



::-.-. . 



do 



i : 



do 



Fair 









" '■•'" 





<F. 



: ". 









v 



37 



N 



:-: 



May 13 



:r 



32 



: 



1: 



": 



fi 



-\ 





:• 



O 



--■- 



:•: 





7 



H 



:: 



37 



:I 



12 



19 



:" 



:: 



----- 



Li 



:•: 



:> 



a 



/ 



:■: 



:: 



37 



a 



= ■ 



l; 



.. 



- 



-:1 



~^- 



; 



& 



:•: 



fi 



Kl 



■ 



.-- 



:.: 



*: 



I 



8 



-\ 



:.; 



-.: 



s 



6 



.: 



71 



-:- 



I 



:: 



a 



- 



's 



-:' 



:■""' 



s 



:-: 



, ; 



51 



24 



. 



* 



:•: 



5Z. 



V. 



30 



70 



39 



y— 



17 



51 



» 



* 



X~ 



16 



r.Ti; 



do 



: .-_-. 

 : 

 do.... 



I 

 do.... 



do.... 



do.... 



Cloud v.. . 

 do*.... 



1-^ 



v. 



:: 

 v: 



-■: 

 *: 



73 



z 



m 



-, 

 ■- 

 -., 

 ". 



:■' 



:'- 

 -.' 



•J". 





.. 



w. 



B 



:Z 



:•! 



5~. 



: ' 



."I 



50 



II 



:■: 



5Z 



60 



EZ 



- 



17 

 13 



:: 



-4 



-.- 



-Z 



DTF1UENCE OF TEMPERATURE ON DIFFUSION, 



Directly and indir- ctly, :emperature is responsible for the destruc- 

 tive abundance of Toxoptera graminurn 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 egga 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 can 

 by its occurrence in the Northern States, where in fairly severe win- 



- it probably winters over in the egg stage only. For this 

 reason the authors have thought investigations of the egg and 

 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 spec: 



The temperatures prevailing over the country where Toxoptera 

 has worked its rz si aerioos ravages, and departures from the normal 

 during the season of grea* tzvity are all given on the tempera- 



ture diagrams. Nos. I to V (pp. 15,21 _ ' _ S, 28). The upper numbers 

 indicate the normal temperature, the lower the departure therefrom 

 (• * — " meaning above and * ' — " below ). Each separate page rel 

 to one of each of the five consecutive outbreaks. From these it will 

 be seen that outbreaks of Toxoptera have succeeded only winters with 



