53 



this kind of investigation with comparatively small numbers of vari- 

 able data. 



If we compare Plots 2 and 3 for the first digging only, with a 

 view to a judgment of the relative efficiency of the 20-inch and the 

 16-inch diskings we shall find that Plot 3 (16-inch disk) shows an in- 

 crease over Plot 2 (20-inch disk) of 34 per cent and 48 per cent in the 

 number of hills infested by ants and by aphids respectively, and a dif- 

 ference of 13 per cent and 35 per cent in the respective numbers of 

 these insects themselves. 



Plots 4 and 5 show no difference to suggest any advantages in 

 double disking over single disking, the percentages of increase and de- 

 crease switching back and forth from one to the other in a haphazard 

 way. On the whole, there is clear evidence in the general outcome of 

 this branch of the Bloomington field-experiment that infestation by 

 ants and root-lice is decidedly reduced by deep plowing and repeated 

 deep disking as a preparation for planting to corn. 



EFFECTS OF TREATMENT AS SHOWN BY NOCTURNAL 



MOVEMENTS OF THE ANTS 



Another branch of the work of Sanders and Flint, which was 

 done largely at night by the aid of dark lanterns used in watching the 

 movements of the ants, threw new light on the efficiency of these 

 methods and led to the amendment of our experimental program for 

 the following year. The freedom and activity with which the corn- 

 field ant moves al)out thru the loose earth in a recently cultivated 

 field, and the long journeys which whole colonies readily make under 

 ground to escape from a disturbed situation to a stable one, carrying 

 with them their entire stock of root-lice and ant larvae, led us to see 

 that these insects are as well adapted to their subterranean life as are 

 their allies to life on the surface or in the open air. 



One of the consequences of this power and habit of free move- 

 ment and migration under ground was that within a month (27 days 

 exactly) after planting, the first three of our narrow plots, that is the 

 check and plots 2 and 3, were in virtually the same condition as to 

 ants and aphids. Plots 4 and 5, originally the most affected by the 

 treatment, alone showed any noteworthy difference from the check in 

 the degree of infestation. According to counts made August 18, these 

 latter plots, taken as one, were shown still to differ from the check by 

 a decrease of 14 per cent and 19 per cent in the number of hills in- 

 fested by ants and aphids respectively, and by 20 per cent and 32 per 

 cent in the number of ants and aphids themselves. The corresponding 



