142 
Psyche 
[September 
dust particles are also trapped in these mats and earlier examinations 
had failed to distinguish between the dust particles and the pollen 
grains. But since pollen grains are often present in the basal hair mats 
on the leaves of Q. emoryi , the stripping of the hairs by the t exanus 
workers becomes understandable. The hairs are removed in the process 
of extracting pollen grains from among them and after the pollen 
grains are extracted the hairs are discarded. Further, if a leaf contains 
no pollen grains the ants should not be overly interested in it. An 
excellent example of this had been furnished by the young oak leaves 
which unfolded in the aquaria. Since these leaves had developed in 
a sealed space they contained no pollen and as a result the ants paid 
scant attention to them. In addition, the pollen-gathering activities 
of texanus offer an explanation of their preference for nests in live- 
oaks. This preference was pointed out in our 1954 study but no 
attempt was made to account for it. Stellate hairs are present on the 
under surface of the leaves of most live-oaks. Their arrangement is 
highly variable. In O. hypoleucoides Cam., the “silverleaf oak”, these 
hairs give rise to the common name for the plant, since they form a 
dense, silvery, tomentose layer over the entire lower surface of the 
leaf. In Q. emoryi , as already noted, most of the stellate hairs are 
concentrated at the base of the blade. But whatever the arrangement, 
these hairs function with great efficiency as pollen traps, for they are 
sufficiently sticky to hold pollen grains with surprising tenacity. In 
one instance the leaves of Q. hypoleucoides were evenly coated with 
willow pollen over the entire lower surface. After the pollen had 
adhered to the stellate hairs no amount of shaking would dislodge it, 
but it is interesting to note that when these pollen coated leaves were 
placed in the aquaria the texanus workers completely cleared them of 
pollen in a few hours. It is even more interesting to consider the 
advantages of such a pollen trap to a pollen feeder. The catkins of 
live-oaks are produced in the spring and remain on the trees for a 
few days only. The period during which pollen can be taken directly 
from the catkins is, therefore, a comparatively brief one. Unless 
texanus could store pollen, and there is no evidence that it does so, 
it could not live on pollen taken directly from the catkins. This seemed 
so obvious that pollen was not even considered as a possible source of 
food in our 1954 study. But while texanus does not store pollen the 
leaves of live-oak trees do. Moreover, this storage is not selective but 
includes any wind-borne pollen. Thus when texanus nests in live-oak 
trees it is assured of a lasting supply of pollen trapped in the stellate 
hairs on the lower surface of the leaves. 
