face of the plant protect it against the attacks of leaf-eaters; and, further, the extranuptial nectaries divert the ants from the reproductive organs, where they might, in some flowers, rob winged insects, aids to fertilization, of the nectar, without themselves aiding in the pollination.
The protection of the floral nectaries may, however, perhaps he assured by other arrangements still more efficacious and more economical to the plants. The plant, becoming myrmecophobic and protecting its floral nectaries against ants, achieves an economy of nutritive forces. Chevaux defrise, gliding surfaces, bent peduncles, and viscous hairs are the principal defensive provisions against ants.
The sweet extract of aphides, cochineals, and some other insects may be likened to a real animal honey. Hence the origin of the pastoral customs of ants, the establishment of underground and open-air stables, and the effective protection of aphides against their enemies, with the real injurious action of ants to a number of plants.
The instinct of ants leads them to lodge themselves in cavities capable of offering them shelter. Such cavities will be more advantageous to them as they are within reach of the food they seek. Thus, a nectariferous plant visited by ants will soon become a host-plant to them, if it offers a cavity suitable for their accommodation. Such is also the case with a plant not nectariferous, but inhabited by insects that can supply ants with an animal nectar. Ants will then devote themselves to the rearing of those insects in the hospitable cavity. In some cases also, the plant, finding a real advantage in the presence of ants on its surface, differentiates food bodies adapted to furnish them a more abundant nourishment.
The services rendered to plants by ants are of various kinds. In numerous cases ants effectually protect the host-plant against the attacks of parasitical insects or the teeth of herbivorous animals; in host-plants with cavities converted into stables ants may attenuate the damage committed by aphides or cochineal insects by removing them from the young organs when their presence would be injurious to a point where it is more compatible with the life of the plant. There is established a kind of symbiosis of these—the ants protecting their cattle which furnish them food, and diminishing the damage occasioned by the herds to the plant on which they feed. Sometimes, but rarely, the refuse material accumulated by the ants in the sheltering organs of the plant seems capable of furnishing it with nutritious matter; but this has yet to be proved in most cases.
The irritation produced by the ants upon the sheltering organ may, by determining a more or less notable increase of that organ,
