1926] Sequential Distribution of Formica exsectoides Foret 149 
does not seem to account for these exceptional cases. House 
rubbish has been dumped in adjacent regions. 
The interrelation of tree and ant is thus a sequential one, 
the young tree supplying food, the older tree deterrent to breed- 
ing by shading the mound. On the other hand, the result for 
the trees of the ant’s activities is partly the furnishing of some 
protection by the removal of injurious insects but also conversely, 
defense of some enemies of the tree and in part, the destruction 
of gome trees that may too soon shade the mound. Yet in the 
long run this association allows the trees to become mature, thus 
driving the ants to new regions of less shade; mounds dying off 
and new ones being made near by till some of them eventually 
become established in regions adjacent to trees but not over- 
shaded by trees. 
In the natural succession of forests it may be that the 
position occupied by Formica exsectoides is that of a dependent 
upon conditions in which the forest is temporarily interrupted or 
destroyed as by fire or wind or small areas of defective soil and 
that with eventual maturity of forest the ants must move grad- 
ually in the course of very many years from place to place. 
Human intervention while tending eventually to eliminate 
Formica exsectoides may in some cases supply favorable con- 
ditions, as in mining and deforestation operations and in aban- 
donment of old fields to new growths as well as in actual planta- 
tion of trees. 
There is a general parallelism between the periods of time 
required for many trees to reach maturity, and the presumed 
length of existence of mounds of Formica exsectoides, thirty 
years and more. The ultimate extinction of the community 
living in any one mound may be brought about naturally by the 
failure of that community to perpetuate individuals, to replace 
those dying from accident and from old age; and this may be 
due partly to lack of ability of the ants to obtain food sufficiently 
from the crowns of old trees and partly from the lack of adequate 
temperature for successful rearing of many young when the op- 
timum temperature is reduced by the shading of the mound by 
old trees. 
