io8 
Journal of Agricultural Research 
Vol. XIV, No. a 
The relation between temperature and immature stages is still more 
clearly brought out by comparing the average length of the immature 
stages of each series with the average mean temperature of the period dur¬ 
ing which each series was conducted. This comparison is well illustrated 
in figure 7. By referring to this diagram it will be noted that there was 
a marked shortening in the length of the immature period as the tem¬ 
perature of each month became higher until the month of June was 
reached. The length of the immature period in August was about the 
same as that for June when the temperature was becoming higher. 
The temperature curve 
and immature-period 
curve crossed in April. 
From this we may 
conclude that the 
length of the imma¬ 
ture period is marked¬ 
ly affected until a 
certain point is 
reached, after which a 
higher temperature 
apparently has little 
or no effect in short¬ 
ening the length of 
this period. 
It is quite probable 
that had the experi¬ 
ments been carried on 
as originally planned, 
Fig. 7. —Graph showing effects of temperature upon length of imma- the immature-penod 
ture period of Toxoptera graminum, plotted against the mean date of curve would Show an 
the immature period. 
upward course after 
August and the temperature curve a downward course, the two curves 
crossing later on in the fall of the year. 
In figure 8 the length of the immature period of the individuals is 
plotted against the mean temperature for the period during which the 
experiments were in progress. 
REARING METHODS 
In conducting the life-history studies of this species 6-inch flowerpot 
cages supplied with lantern chimneys covered with cheesecloth were 
utilized. Oats were used as host plants throughout the year. These 
cages were all kept under normal conditions throughout the year in an 
outdoor breeding shelter (Pi. 12, A). The curtains of this shelter were 
partly raised during sunny days to admit the warm sun’s rays. Care 
was taken, however, that the rays did not strike the chimney covers as 
