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ANTS AND PLANT-STRUCTURE 407
[When I compare these and similar instances
with the Pitchers of the Nepenthes, in which (as
I
learn from the accounts of travellers) ants as well as
water are nearly always found,
I cannot doubt that
those curious appendages have attained their actual
dimensions through the deepening 'and widening
which they have undergone from ants through
untold ages.]
We have a curious example, in the genus
Cinchona, of the supposed correlation of a minute
structural peculiarity with chemical and medical
properties. Eminent botanists, 'such as Weddell
and Karsten, who have studied that ^enus in its
c>
native forests, have thought they had found a char-
acter in the leaves always associated with a bark
rich in alkaloids, viz. the presence of a small pit or
scrobicule in the axil of each vein on the underside
of the leaf. But when good specimens of C. sitc-
cirubra, the richest of all the barks in alkaloids,
came to be examined, the leaves were found entirely
destitute of scrobicules ! See now how this comes
about. The leaves of the Hill Barks those, namely,
that grow at an elevation of 8000 feet and upwards
are liable to be infested by a small mite which
nestles in the scrobicules has caused them, in fact-
its remote ancestors having at first sheltered in the
vein-axils but C. succirubra ; grows always below
that elevation indeed, as low down as 2400 to 6000
feet and is the only quinine-producing Cinchona
that descends so low, the other species of Cinchona
that grow at a low elevation having all medically
worthless bark. But as all these species, C. suc-
cirubra included, are equally destitute of scrobiculate
leaves and of mites, the reasonable inference is that