which--according to the researches of A. Moller--serves as the
substratum for a special fungus (_Rozites gongylophora_), the staple
food of the ants. The insects cultivate their fungus, weeding out mould
and bacterial growths, and causing the appearance, on the surface of
their "mushroom garden," of numerous small white bodies formed by
swollen ends of the fungus hyphae. When the fungus is grown elsewhere
than in the ants' nest it produces gonidia instead of the white masses
on which the ants feed, hence it seems that these masses are indeed
produced as the result of some unknown cultural process. Other genera of
South American ants--_Apterostigma_ and _Cyphomyrmex_--make similar
fungal cultivations, but they use wood, grain or dung as the substratum
instead of leaf fragments. Each kind of ant is so addicted to its own
particular fungal food that it refuses disdainfully, even when hungry,
the produce of an alien nest.

_Guests of Ants._--Many ants feed largely and some almost entirely on the
saccharine secretions of other insects, the best known of which are the
Aphides (plant-lice or "green-fly"). This consideration leads us to one
of the most remarkable and fascinating features of ant-communities--the
presence in the nests of insects and other small arthropods, which are
tended and cared for by the ants as their "guests," rendering to the ants
in return the sweet food which they desire. The relation between ants and
aphids has often been compared to that between men and milch cattle. Sir
J. Lubbock (Lord Avebury) states that the common British yellow ants
(_Lasius flavus_) collect flocks of root-feeding aphids in their
underground nests, protect them, build earthen shelters over them, and
take the greatest care of their eggs. Other ants, such as the British
black garden species (_L. niger_), go after the aphids that frequent the
shoots of plants. Many species of aphid migrate from one plant to another
at certain stages in their life-cycle when their numbers have very
largely increased, and F.M. Webster has observed ants, foreseeing this
emigration, to carry aphids from apple trees to grasses. It has been
shown by M. Busgen that the sweet secretion (honey-dew) of the aphids is
not derived, as generally believed, from the paired cornicles on the
fifth abdominal segment, but from the intestine, whence it exudes in
drops and is swallowed by the ants.

Besides the aphids, other insects, such as scale insects (_Coccidae_)