MESSMATES, MUTUALISTS, AND PARASITES 83 
big stomata [ze. pores in the epidermis] on the overlapping 
scales of the still-closed heads in such quantities that one can 
see a drop of it on every scale in the early morning, whilst 
later in the day, as the water evaporates, little masses, or even 
crystals, of sugar are to be found. This sugar, either in its liquid 
or solid form, is very palatable to the ants, which habitually resort 
to these heads during the period of its secretion. And to pre- 
serve it for themselves they resent any invasion from outside. 
If one of the aforementioned beetles appears they assume a 
menacing attitude. They hold on to the involucral scales with 
their last pair of legs and present their fore-legs, abdomen, and 
powerful jaws to the enemy, as shown in the figure. Thus they 
remain till the beetle withdraws, if necessary hastening its retreat 
by squirting formic acid in its direction. Then they quietly begin 
to feed on the honey again.” 
Much has yet to be learnt about the relations between British 
plants and insects in the present connection, and no undoubted 
case of ant-guards has so far been described. Some of our 
native trees, however, harbour mites that appear to discharge 
defensive duties. Scott Elliot (in Mature Studzes) thus speaks 
of them:—“ Almost any common tree, such as the Lime, Ash, 
Elm, or Horse-Chestnut, will show on the lower side of the leaves 
little hairy patches which occupy the forks of the veins. If these 
are examined in summer with a strong magnifying glass, and 
stirred up with a pin, very small active . . . mites will be found. 
They run about quickly, and once seen, can be observed 
with ease, whenever looked for. The hairy grottoes which they 
inhabit are often rather neatly formed; but they are difficult to 
describe. As a rule the colour of the mite is that of the hairs 
amongst which it lives. These mites come forth at night, and 
appear to live upon bacteria and upon the spores of fungi, lichens, 
or alge. But here again it is not possible to give as exact details 
as would be desirable.” The arrangement described is of special 
interest, as it appears to be a case of animals defending a plant 
against other plants lower in the scale. 
Tue PotiwaTion or Fiowers sy AnimaLs.—Of all the 
numerous kinds of relation between plants and animals none 
has attracted more attention than the one now to be briefly de- 
scribed. So much is this the case that, though of absorbing 
interest, it is almost in danger of becoming hackneyed. But 
