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ANTS AND PLANT-STRUCTURE 391
of Tococa, however, are inhabited by ants of medium
size, with a blackish or brownish abdomen and pale
thorax, and a milky fluid exudes from them when
crushed ;
they bite but do not sting.
T. macrophysca, Benth. (Spruce, 2188), grows in
moist caatingas of the Rio Negro and Uaupes, and
has leaves sometimes a foot long, not very unequal,
and all of them usually bearing a stout elongatocuneiform
sac, an inch long, at the top of the
petiole.
Tococas are scattered over the Amazon region
from the sea-coast to the roots of the Ancles, and
two species T. , ( pterocalyx sp. n., and T. parviflora,
sp. n.) ascend the Peruvian Andes to 2500-3000
feet. I gathered altogether twenty-four or twenty-
five species of Tococa, and all but one or two (T.
planifolia, Benth., and a closely -allied species or
variety) have sacs on the leaves inhabited by ants.
An examination of the circumstances of growth of
the esaccate T. planifolia seems to throw light on
the origin of sacs on the leaves of the other
species.
Tococa planifolia grows here and there along the
shores of the Rio Negro, at least as far up as to
the foot of the cataracts, or say for about 700 miles.
From the cataracts upwards, on the main river, on
its tributary the Uaupes, and on some clear-water
affluents of the Casiquiari, it is replaced by an
allied non-sacciferous species or possibly a mere
variety. Wherever it grows, it always occupies the
very edge of the riparial forest, to which it forms
an inner fringe, along
with various Rubiacese,
Apocynese, etc., of similar humble growth,
all ot
which are completely submerged in the time of flood ;