60 
Psyche 
[June 
viding ridge has many shrubby live oaks on its southeastern 
slope. These are very abundant at the base of the ridge but 
thin out toward its crest. A few oaks cross the crest of 
the ridge into the smaller valley but most of this valley, 
particularly its slope which faces southeast, is dominated 
by numerous plants of Agave palmeri. As the agave plants 
are much less abundant in the larger valley, the two sides 
of the ridge present a very different appearance. Despite 
this striking vegetational difference the two areas are part 
of the same plant association. Shreve has pointed out (7) 
that in the southern Arizona mountains the evergreen oak 
forest is an open community with many other plants pres- 
ent, among them Agave palmeri. Shreve’s view is fully 
supported as far as the ants in this area are concerned, 
for the same ants occur in the dense oak thickets and on 
the open slopes where the agave plants grow. In both these 
areas the soil is very stony, with many of the stones partly 
projecting above the surface. The nests of ulcerosus are 
usually situated under such partially buried stones. 
Considering the abundance of the foraging workers, the 
nests of ulcerosus are extraordinarily difficult to find. Mr. 
Luther Little, who was camping with us, first called my 
attention to the workers of ulcerosus on the agave leaves. 
So many of the plants were visited by foraging workers 
that I thought that there would be little trouble in tracing 
them to their nests. Most ants readily accept termites offered 
to them and carry them at once to their nests. I repeatedly 
offered termites to the workers of ulcerosus which they ac- 
cepted readily enough. But, instead of taking them home, 
they usually sucked the juices from the termite and re- 
mained on the agave leaf. In a few instances a worker 
would start home with the termite, but nothing came of 
this for the ant would soon drop the termite and return to 
the agave leaf. Although the slope of the canyon was cov- 
ered with agave plants in all stages of development, the 
ants chose only those plants which had recently bloomed. 
Young plants were never visited, nor were the shrivelled 
remains of plants which had bloomed in previous seasons. 
The heavy panicle of fruit, towering ten to twelve feet above 
the leaves seemed the part most likely to attract the for- 
