BIOLOGIC RELATIONS BETWEEN PLANTS AND ANTS. 453 



second, by diverting from the reproductive organs ants that otherwise, 

 in certain flowers, might steal the nectar, thus depriving winged insects 

 of it without aiding in pollination. 



But the protection of the floral nectaries may be assured by other 

 arrangements still more efficacious and more economical for the plant. 

 By becoming myrmecophobic and keeping its floral nectaries away from 

 the ants the plant economizes its nutritive materials. Chevaux de frise, 

 slippery surfaces steep peduncles, and viscous hairs are the principal 

 myrmecophobic features. 



We may consider as a true animal honeydew the sugary excretion of 

 plant lice, cochineals, and some other insects. From this arise the 

 pastoral habits of ants, the establishment of subterranean and aerial 

 stables, and the effective protection of the plant lice against their 

 enemies; hence occurs a real injury to a number of plants indirectly 

 caused by ants. 



The instinct of ants leads them to lodge themselves in some cavities 

 capable of offering them shelter. These cavities will be more advan- 

 tageous to them in proportion as they are within reach of the food they 

 require. So, if a- nectariferous plant visited by ants has a suitable 

 cavity, it will soon become a lodging plant for those insects. Such is 

 also the case with a nonnectariferous plant inhabited by insects capable 

 of furnishing nectar to ants. The ants will then occupy themselves 

 with the rearing of such animals within the lodging cavity. In certain 

 cases, also, when a plant finds a real advantage in the constant presence 

 of ants on its surface, it will differentiate "food bodies" suitable for 

 furnishing them with a more abundant aliment. 



The services rendered to plants by ants are of various kinds. In a 

 number of cases the latter effectually protect the host plant against 

 the attacks of parasitic insects or the teeth of herbivora. In the case of 

 lodging plants with cavities arranged for stables the ants may min- 

 imize the injuries inflicted by plant lice and cochineals by transporting 

 them from young organs, where their presence would be injurious, to 

 localities upon the vegetable where their presence would be more com- 

 patible with the life of the plant. There is thus established a sort of 

 triple symbiosis, the ants protecting their flocks that furnish them food 

 and diminishing the injuries occasioned by those flocks upon the plant 

 on which they feed. Sometimes, but rarely, the detritus accumulated 

 by the ants in the lodging organ seems to serve as a nutritive material 

 for the plants. This, however, remains to be demonstrated in most 

 cases. Finally, the irritation caused by the ants upon the lodging organ 

 may, by determining a greater increase in its growth, assist the plant 

 in its struggle with rival species or with physical agencies. 



The primitive origin of the lodging organ varies, in fact, in different 

 types. Sometimes the ants make use of closed or nearly closed cavities 

 forming a part of the morphologic plan of the plant, and having a merely 

 mechanical function (hollow internodes, being lighter, economizing 



