ANTS AS THE GUESTS OF PLANTS. 829 



face of tlie plant protect it against the attacks of leaf-eaters; and, 

 further, the extranuptial nectaries divert the ants from the repro- 

 ductive 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 econ- 

 omy 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 in- 

 sects may be likened to a real animal honey. Hence the origin 

 of the pastoral customs of ants, the establishment of under- 

 ground 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 ad- 

 vantageous to them as they are within reach of the food they 

 seek. Thus, a nectariferous plant visited by ants will soon be- 

 come a host-plant to them, if it offers a cavity suitable for their 

 accommodation. Such is also the case with a plant not nectar- 

 iferous, 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 sur- 

 face, 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 ani- 

 mals ; 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. 



