vii Relations Between Plants and Animals 131 



tions due to the symbiosis. " Of late," he says, " naturalists 

 have become more and more accustomed to interpret all 

 structural peculiarities which are seen to be useful for a 

 certain purpose, as if they had originated for that pur- 

 pose." This Schimper rightly regards as unscientific. All 

 such interpretations must rest on observation and experi- 

 ment. 



Many ants live in the nooks which plants often afford 

 in the axils of leaves, among the tangled roots of epiphytes, 

 inside old galls, and so on ; others build nests which they 

 fix to the branches; others bore labyrinthine passages in 

 the dead bark of trees. "The fanatics of biology" (i.e. 

 bionomics) " are inclined to find adaptations in all such cases 

 of constant or usual symbiosis. The chambers of Tillandsia 

 bulbosa, the feltwork of aerial roots in the case of many 

 epiphytes, the cavities of the stem and branches in Triplaris, 

 are all for the reception of the protective ants. But we 

 know that these structures have quite another meaning : 

 the cavities in the base of Tillandsia are dried-up cisterns, 

 the feltwork of aerial roots collects moisture and humus, the 

 hollow stems of Triplaris serve to combine maximum elas- 

 ticity with minimum material." 



Where it can be shown that certain plants of which the 

 leaf-cutters are fond have a bodyguard of ants, there is no 

 reason to doubt that these are of protective advantage. 

 This has been repeatedly proved by observation, especially 

 in the case of some species of Cecropia (Imbauba or trumpet 

 tree). These trees have smooth upright stems, raised on 

 short aerial roots, and bearing simple branches, the whole 

 appearance suggesting a gigantic candelabra. The leaves 

 are few but very large. Now when one shakes a branch of 

 the Cecropia, one rouses a wild army of ants, which with 

 poisonous jaws resent the intrusion. Where do they all 

 come from ? Closer inspection shows little round apertures, 



