MESSMATES, MUTUALISTS, AND PARASITES 81 
certainly to be regarded as a means of defence against wood- 
boring insects, especially beetles. The many varieties of resin 
and gum are also of protective nature. 
We have already had occasion to note (vol. ii, p. 301) that 
quite a number of animals advertise their disagreeable properties 
by conspicuous colours or by other means. Such warning colora- 
tion also appears to be present in certain plants, as, for instance, 
in some of the poisonous toad-stools, 
which are of glaring and repulsive 
appearance. And here also it would 
seem that, as among animals, cases of 
Mimicry are to be found, for some 
harmless toad-stools closely resemble 
their poisonous brethren, and thus 
gain some amount of protection. The 
highly desirable Boletus edulis, for ex- 
ample, is very liable to be mistaken 
for its virulently poisonous cousin (2. 
Satanas). 
Another set of plants contain aro- 
matic or fragrant essential oils which, 
though pleasant enough to our own 
sense of smell, act as deterrents to 
many animals. Such are sage, mint, 
lavender, and many spice-producing 
forms. 
There is still another means of 
defence, and one which is more M- 4. sors <ncads tAceiberoentelal, poe 
teresting from the zoological stand-  sessinghollow thoms in which ants finds shelter, 
point than those so far described. eae art ‘ 
Certain forms are known which may appropriately be termed 
ant-loving (myrmecophilous), because they maintain a “ police- 
force” of ants, by which they are protected from leaf-cutting 
insects and other unwelcome visitors. The services of these 
hirelings are secured by means of material benefits of substantial 
character. A well-known case is that of a sort of Acacia (Acacza 
spharocephala, fig. 1076), which bears little pear-shaped “ food- 
bodies” to appease the appetites of its retainers, and also hollow 
thorns which furnish them with shelter. Another curious instance 
is afforded by a kind of Oak (Quercus pubescens) in which a gall- 
VoL. IV. 100 
