130 



not sufficiently protected by their long, sharp thorns from the 

 browsing animals.^ 



Are the Acacias Myrmecophilous ? 



After presenting all the essential facts, so far as known, 

 concerning the acacias and their ants, we are prepared to consider 

 the question as to whether these plants are actually m\Tmeco- 

 philous, as implied in the Belt-Delpino hypothesis. In other 

 words, have these plants developed their extraordinary thorns,, 

 extrafloral nectaries, and Beltian bodies for the purpose of insuring 

 the presence of a body-guard of stinging ants ? It is certain 

 that acacias that are quite free from ants grow and flourish 

 quite as well as ant-infested individuals, and produce the thorns, 

 nectaries, and Beltian bodies in a perfectl}' normal manner. This 

 I have found to be the case in a few localities in Western Guate- 

 mala, and also, under interesting circumstances, in the banana 

 plantations about Quirigua. In the latter locality the negroes, 

 while making clearings, had carefully lopped off all the branches, 

 of many of the old acacias, leaving only their stumps. These 

 had then put forth vigorous young branches, which, however,, 

 were quite free from ants, evidently because they had grown 

 out, and their spines had matured at a time when the recently 

 fecundated Psendomyrma queens were not fl\ing about in search 

 of nesting sites. Finally, attention may be again called to the 

 fact that the very young acacias, which would seem to require 

 the greatest amount of protection, are either entirely free from 

 ants, or contain only young queens hidden away in the hollow 

 thorns. 



^ Since the foregoing paragraphs were written, Dr. Glover Allen, of the 

 Boston Society of Natural History, has, at my request, made some inter- 

 esting observations on the enlarged thorns of Acacia fistula in the Blue 

 Nile and Dinder River Valley, while accompanying Dr. J. C. Phillip's 

 Sudan Expedition. On cutting open very young thorns, which were 

 only slightly swollen at the base, he found them to consist " of a solid 

 mass of green, succulent tissue, with a single small larva inside, as in a 

 typical insect gall." This larva seemed to be that of some Hymenopterous- 

 msect. His observations, which will be published in detail later, show 

 very clearly that the enlarged thorns are not only galls, which are formed 

 independently of the ants, as Sjöstedt observed, but that these structures 

 are inhabited by very few ants during January and February. 



