XXIV 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 elongato- 
cuneiform 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 Andes, and 
two species {T. pterocalyx, sp. n., and T. parvifiora, 
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 Rubiaceae, 
Apocyneae, etc., of similar humble growth, all of 
which are conpletely sub7?ierged in the time of flood ; 
