Chap. VI] ANIMALS 153 



Most plants provided with ant-dwellings at the same time supply food to their 

 protectors, usually in the form of a sugary liquid in extra-Moral nectaries. A 

 very great number of plants, especially in the tropics \ possess such nectaries 

 without at the same time providing dwelling-places for the ants. Nevertheless 

 some naturalists, especially Delpino, regard all such structures as allurements to 

 protective ants, an opinion which is clearly untenable when we bear in mind the 

 frequent occurrence of extra-floral nectaries and the rarity of observations on 

 their efficiency in inducing ants to protect plants. It is however proved that 

 protection is afforded in certain cases. Thus, when at Blumenau in Southern 

 Brazil, I was able to observe how ants, which there very commonly visited 

 Cassia neglecta in order to suck the sweet liquid excreted by nectaries at the 

 base of the petiole, put to flight marauding leaf-cutting ants 2 , though they did 

 not interfere with a beetle that was usually present. In like manner R. von 

 Wettstein proved experimentally in the case of Jurinea mollis, and Burck in 

 several plants in the Buitenzorg botanic garden, that unwelcome visitors were 

 kept away from the flowers by the ants. On the other hand, I have not been 

 able to prove visits by ants to several species of plants provided with extra-floral 

 nectaries. 



The most probable view at present appears to be that extra-floral nectaries 

 fulfil a still unknown function, which is independent of the ants, but is in some 

 way connected with a warm climate, and that they have only secondarily become 

 myrmecophilous organs, just like Belt's and Miiller's corpuscles or the structures 

 rich in albuminoids that Burck found on Thunbergia. 



We may, in the first place, tentatively regard as allurements selectively adapted 

 to ants and as extra-floral nectaries modified for this purpose, these structures 

 that are characterized by their size, striking colour, excretory activity, by their 

 congregation near the flowers, and especially by the great assiduity with which 

 they are visited by ants ; but only the proof that ants afford an essential protection 

 to the plant will give a firm basis to this hypothesis. On the other hand, it is 

 to be hoped that success will be attained in discovering what was the original, 

 and in many cases is still the exclusive, significance of the nectaries. That this 

 is not a case of any very essential function is proved by experiments made 

 with plants of Cassia neglecta which I deprived of all their nectaries, without 

 doing them any injury. The wounds healed quickly and excreted no sugar, so 

 that the function in question might be considered as being completely in abeyance. 

 Unfortunately there was not time to ascertain whether the plants, thus deprived 

 of their nectar and no longer visited by the protective ants, became victims to 

 the leaf-cutters. 



1 Complete references in Delpino. 



2 Schimper, op. cit, p. 68, Plate iii. fig. 9. 



