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 (B. 

 Sat anas). 



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 in- 



tereStinP" from the ZOOlogical Stand- 



r , ., 



point than those so far described. 

 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 (Acacia 

 sphczrocephala, 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- 



Fig. 1076. Acacia (A, spfuerocepnala), pos- 

 sessinghollow thorns in which ants finds shelter, 

 and pear-shaped food-bodies on tips of leaflets. 



VOL. IV. 



100 



