1926] Sequential Distribution of Formica exsedoides Forel 139 
shade or jutting up into the sunshine. In a crowded stand of 
such trees each may have 12 square meters area of leaf. Each 
of these crowded trees may then expand three times as much 
leaf area as when young but it will be perhaps six times as high 
as when young: thus the ant to get all over its green leaves will 
have to run up twice as much trunk as when the tree was young. 
We conclude that as long as the trees are young and have not 
crowded one another and have plenty of sunshine their combined 
leaf surface within the ant’s walking distance to its mound will 
be greater than when these trees have grown crowded and tall, 
since the stems of the trees increase more rapidly in height than 
the entire leaf area expands. 
In endeavoring to apply the above considerations to the 
observed changes in distribution of the ant mounds we observe 
that in the fifteen years the trees of the old wood in the north- 
west area had grown older and the ground more densely shaded, 
and the ants had not increased. 
In the middle region where in 1905 the earth was quite bare 
and very poor dump, spread out in a plain of several acres, there 
had grown up more and more young trees, especially black locust, 
gradually encroaching from the edges over more and more of the 
bare area along with coarse grass and brambles and Japanese 
honeysuckle. In this region the new ant mounds became very 
abundant. 
Again in the region of the “village”, where in 1905 trees were 
few and far from the two old mine holes that were grass-grown, 
there sprang up more and more young trees and here again the 
number of ant hills greatly increased. 
On the other hand, in the region where the large “stone 
house” group of mounds had been in 1905 there was no increase 
and no new trees, and besides the fields were cultivated and 
there was some passing of vehicles along the wood edge. 
Also the diminution along the older roads to the east may 
have been due to the fact that trees had grown larger so that 
there may not have been as good feeding conditions here, in 
1920, as formerly. 
There seems to be some correlation between the success of 
new mounds and the presence of young vigorous trees, and some 
