Chav. VI] ANIMALS 153 



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

 protectors, usuallj' in the form of a sugarj' liquid in extra-floral nectaries. A 

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

 vvithout 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 wlien wc bear in mind the 

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

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

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

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

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

 jase of the petiole, put to flight marauding leaf-cutting ants^ though they did 

 lot interfere with a beetle that was usuallj' present. In like manner R. von 

 ^Vettstcin proved experimentally in the case of Jurinea mollis, and Burck in 

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

 cept away from the flowers bj' the ants. On the other hand, I have not been 

 ible to prove visits b}' ants to several species of plants provided with extra-floral 

 lectaries. 



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

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

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

 nyrmecophilous organs, just like Belt's and Mtiller's corpuscles or the structures 

 ■ich in albuminoids that Burck found on Thunbergia. 



We may, in the first place, tentatively regard as allurements selectivel}' adapted 



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



hat are characterized by their size, striking colour, excretory activitj', by their 



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



hey are visited by ants ; but only the proof that ants aftbrd an essential protection 



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



D be hoped tliat success will be attained in discovering what was the original, 



nd in manj' cases is still the exclusive, significance of the nectaries. That this 



not a case of any very essential function is prov-ed by experiments made 



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



oing them any injurj'. The wounds healed quickly and excreted no sugar, so 



lat the function in question might be considered as being completely in abej-ance. 



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



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



le leaf-cutters. 



' Complete references in Delpino. 



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



