RELATIONS OF ANTS TO VASCULAR PLANTS. 299 



floral nectaries are regarded as alluring organs and volumes have been 

 written on the insects and birds that visit them. In these works, how- 

 ever, the ants are not seriously considered, probably because they treat 

 the flowers very cavalierly, for, unlike the bees, they do not concentrate 

 their attention on particular plants and make cross-fertilization one of 

 their main avocations. 



2. Extrafloral, or Extranuptial Nectaries. These organs which, 

 like the floral nectaries, secrete a saccharine liquid, are situated on the 

 most diverse portions of the plant body, and occur in hundreds of 

 species, both among ferns and flowering plants. 1 While there can be 

 no doubt that in many of these plants the extrafloral nectaries are 

 assiduously visited by ants, it by no means follows that these organs 

 have been developed for the purpose of attracting these insects. 

 Indeed, it must be admitted that the significance of the nectaries of 

 this type is far from clear. Some botanists, like Bonnier, Johow, 

 and Lloyd, believe that they may be excretory organs and that 

 the excretion is carried off in small quantities dissolved in the liquid 

 nectar. It has been noticed that the organs in question are sometimes 

 developed only on young leaves, as in the poplar and brake fern, and 

 that the formation of sugar is in all probability the result of more 

 active metabolism in the surrounding tissues or due to other unusual 

 physiological conditions of rapid growth. The excretion thus formed 

 is then utilized by ants and many other insects (wasps, flies, beetles, 

 etc.). This sober physiological explanation is rejected by Schimper 

 (1888) and others on the ground that the excretory function of these 

 nectaries has never been proved. They are therefore interpreted as 

 alluring organs devised especially for ants and scattered over the sur- 

 face of the plant for the purpose of extending the surveillance of these 

 insects. Their development on the young leaves is said to be only what 

 we should expect, for such parts would be in greatest need of protection 

 from injury or defoliation. Even Schimper, however, is compelled to 

 admit that this view of the extrafloral nectaries can be accepted only if 

 it can be proved, " first, that the visitations of the ants confer protec- 

 tion on the plants with extranuptial nectaries and that in the absence 

 of the insects a much greater number would perish or fail to produce 

 flowers or set seeds, than when the insects are present, and second, that 



1 The following is a list of some of the genera that comprise species with extra- 

 floral nectaries: Pteris, Polypodiuin, Acrostichum, Popuhis, Ouercus, Paonia. 

 Rliipsalis, Sarraccnia, Darlingtonia, Gossypium, Psidium, Balsamina, Vicia, Pha- 

 seohis, Dolichos, Lablab, Cassia, Acacia, Erythrina, Canavalia, Ailanthus, Rosa. 

 Cratccgus, Primus, Syringa, Passiflora, Sambucits, Viburnum, Luff-a, Impatient. 

 Mclampyntm. Turncra, Crozophora, Marcgravia, Stillingia, Alchorca, Ricimts, 

 Ccn la it rca . H elia nth us. 



