434 BIOLOGIC RELATIONS BETWEEN PLANTS AND ANTS. 



abortive attempts at penetration made by the ants, the resistance of 

 the tissues there having caused them to abandon the effort, which, how- 

 ever, easily succeeds at the upper part of the internode, where, from an 

 early age, the medullary tissue is less dense and the peripheral tissues 

 less resistant. Perhaps the irritation produced by the ants may cause 

 an increase in the diameter of the intern odes and of their cavity. 



The ants doubtless render to the Kibaras services of various kinds; 

 first, protection against plant eaters; then transportation of the cochi- 

 neals to a location where they will be less injurious than upon the 

 young and undeveloped parts; finally, fertilization of the flowers. 



The Kibaras are, in fact, monoecious, and their floral structure is 

 such that their fertilization seems impossible without the intervention 

 of insects. In exchange for these services they offer these ants a cavity 

 for lodgment, and very likely an aliment indirectly furnished by the 

 cochineals. 



The Cecropia adenopus is a plant of Brazil, belonging to the Aralia- 

 cea?, that in its native country bears the name of Amboiba or Imbauba. 

 As long ago as J 648 Marcgrave said of it " Totus intus cavus a radice 

 ad summum usque et cavitas ilia per interstitia semi-digiti ubique dis- 

 tincta et trans versali membraua, in cujus medio foramen rotundum 

 magnitudine pisi. In hac cavitate reperiuntur semper formic?e rubrse 

 ipsa coloris et hepatici." The medullary tissue is narrow at the base 

 of the trunk, enlarging above, and is interrupted at each node by a 

 ligneous disk. Two consecutive disks thus bound a closed cavity cor- 

 responding to an internode. In these cells the ants pursue the culture 

 of cochineals. This is a myrmecophilous feature similar to that which 

 Beccari pointed out in Kibara formicarum and liospitans. Belt and 

 Fritz Miiller have studied the relations of this plant to ants. Accord- 

 ing to the latter author there is a small cavity in the upper part of each 

 internode, where the wall of the internodal chamber is thinner. At this 

 point a pregnant female ant makes a hole in order to penetrate the 

 chamber. These perforations can be plainly seen in herbarium speci- 

 mens. Their relative position is perfectly regular, and they can by no 

 means be considered as accidental. The ants once installed in the 

 chambers, perforate the nodal disks and may thus circulate, under 

 shelter, throughout the entire length of the trunk (Belt). Three species 

 of ants frequent the Cecropia, but if either of these species is present 

 the others are not found upon the tree. Fritz Miiller thinks, on the 

 contrary, that perforation of the disks does not take place. These two 

 opinions, apparently contradictory, may perhaps be easily explained. 

 Possibly the various species of ants that frequent the Cecropia may not 

 have identical habits. Some may leave the disks intact, others may 

 perforate them. Each of these observers may have been dealing with 

 a different species of insect. Perhaps, also, they did not observe the 

 same species of Cecropia. The Cecropia adenopus may not be the only 

 one that presents a hollow stem separated into chambers by nodal 



