aid the host-plant in the struggle which it has to sustain, either against rival species or against physical agents.
The prime origin of the host-organ is really variable, according to the types considered. Sometimes ants take advantage of cavities wholly or incompletely closed which are a part of the morphological plan of the plant, and the function of which can only be mechanical, such as hollow internodes; sometimes they convert into ants' nests organs that serve to protect plants against herbivorous animals—thorns; or against physical agencies—reservoirs of water.
In other cases the parasitical origin of the host-organ does not seem doubtful. In some types it may be contrived by the ants in view of their wants—perforation of the wall, formation of galleries; in other cases primarily abnormal dispositions determined by the presence of ants in the host-organs seem to become, through heredity and selection, normal organs; ants then find host-organs all ready to receive them, without their having to perform any labors preliminary to putting them to use. Dispositions favorable to ants are therefore of multiple origin, varying according to the case.
The biological relations between plants and ants come thus, by insensible degrees, to affect the complex characteristics of life in common, to reciprocal advantage—symbiosis.
If we examine the phenomena of the world with the eyes of the ancient naturalist we shall not fail to admire greatly the various means employed by Nature to reach its ends. Regarding the relations of ants and plants with reference to the reason for the existence of biological peculiarities, we shall not be able to appreciate too much the providence which gives ants access to nourishing plants, and furnishes some plants with guests capable of giving them protection in exchange for some small services.
Does it not seem as if each species was created for the destruction of some other one, and that the life of so many individuals of opposing tendencies should ultimately result in the destruction of all that is living on the surface of the globe? Yet strangely from the struggle itself is born accord; the antagonism of beings culminates in symbiosis, instability in equilibrium, death in life. Chaos engenders order. The resultant of these extensive contests, although most usually not appreciable to the eye not forewarned, may be summarized in the word harmony. Perfect accord is established between beings that have nothing in common, precisely in consequence of the diversity of their wants; for in this accord none of the concordants has an interest in despoiling its associate.
By this the law of progress is certainly confirmed as to what concerns general life. Aside from the sufferings and the death of
