APPENDIX 



to such insects. However, the biological connexion which exists in 

 either case between the plants and the ants is similar, being a symbiosis 

 for reciprocal advantage. In the one case as in the other the plants 

 tolerate and act as hosts to the ants, because these insects are useful 

 to them as a defence against other insects and hurtful creatures of various 

 kinds. 



At first I thought that the ants, by the irritation they produced on 

 young budding plants of Myrmecodia, favoured the swelling of the base 

 of the stem, and were the direct cause of such an hypertrophy. Further 

 investigations and researches and the observations of Dr. Treub have, 

 however, convinced me that from the very beginning these swellings 

 appear independently of any action of the ants, and that when the latter 

 are absent the tubers develop much in the same manner. I do not how- 

 ever think it equally certain that ants have no part in the formation of 

 the internal galleries. My observations tend to prove that in some cases, 

 in non-Bornean species of Myrmecodia, 1 ants take an active part in the 

 formation of the galleries and especially in that of the apertures which 

 lead to them. But be this as it may, the hospitating Rubiacece live on 

 a footing of reciprocal utility or mutualism with their inhabitants, 

 which act as a formidable army of defence, for no animal dares to meddle 

 with a plant guarded by a host of biting ants, ready to assault the 

 imprudent invader in myriads. 



The globose form and succulent substance which make the tubers of 

 formicarian Rubiacece resemble big fruits, would be a sufficient attraction 

 to not a. few animals, monkeys for instance, as food ; but it is certain that 

 on account of the ants no animal dares to touch them. I suppose that 

 this is the reason why, in nature, no individual of Myrmecodia or of 

 Hydnophytum is found uninhabited and deprived of its useful dwellers, 

 because undoubtedly in this case it would be immediately destroyed. 

 It remains, however, to be ascertained whether in the natural condition 

 ants, besides serving as an alert militia for the defence of the tubers, 

 confer indirectly some other advantage on the plant which shelters them. 

 Whether, for instance, it is not possible that the mass of detritus, excreta, 

 and humus which the ants accumulate in the galleries, is not utilised 

 for alimentary purposes by the plant. 



In order that such material may be utilised by the plant, the latter 

 must be able to assimilate the nutritive elements from the surfaces of 

 the internal galleries. Now it is true that in the tubers of some species 

 of formicarian Rubiacece, not living in Borneo, I have found on the 

 walls of the galleries small roots, which might serve for the aforesaid 

 function ; but both in the Myrmecodia and in the Hydnophytum of Borneo, 

 no such internal rootlets have been found, although it has been observed 

 that the internal walls of the galleries are dotted with small but numerous 

 cellular prominences similar to so-called " lenticellae " with which, in fact, 

 Dr. Treub has compared them, considering such " pseudo-lenticellse " 

 as aerating organs of the plant. Without wishing to deny this, I cannot, 

 however, exclude the hypothesis that these are more probably subsidiary 

 organs of alimentation, analogous to those which are found in the 



1 In Myrmecodia alata and bulbosa ; Malesia, vol. ii., pi. xxv., xxvi. 



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