132 Chapters in Modern Botany CHAP. 



especially on the upper internodes, which lead into the 

 hollow stem. 



In walking with the well-known naturalist Fritz Miiller, 

 Schimper saw a small Imbauba-tree which had been stripped 

 of its leaves by the leaf-cutters. Fritz Miiller ventured to 

 affirm that in this case the bodyguard must have been 

 absent, and in slicing up the stem he found not one. This 

 was not an isolated case ; the same has been repeatedly 

 observed, so that we may safely conclude that a Cecropia 

 tenanted by its bodyguard is relatively safe from the leaf- 

 cutters. 



The hollow stem with its horizontal partitions is plainly 

 a comfortable home for the protective ants, but does it 

 exhibit any structural peculiarities which must be referred 

 to the insects? This cannot be said of the cavities them- 

 selves, but what of the doors ? Each internode has at one 

 time a door, which is obliterated by subsequent growth. 

 The door is always in the same position ; it is made by the 

 ants at a spot where the wall of the stem thins away in an 

 oval depression, and this is originally due to the pressure of 

 a bud. There is no doubt that the beginning of the door 

 arises quite apart from the ants, but on the other hand 

 Schimper has detected a number of minute structural 

 peculiarities connected with the door which he cannot 

 explain except as adaptations to the visitors. On Cecropias 

 which grow on the hill of Corcovado near Rio de Janeiro, 

 and have very smooth wax-covered skins, ants are unrepre- 

 sented, and the minute structure around the slight depression 

 at which a door, were there one, would be formed, is quite 

 different. 



The ants find shelter within the Cecropia stem, but the 

 tree also affords them abundant food. Near the base of 

 the leaf-stalk there is on the under surface a small area 

 covered with brown velvet-like hair, and on the surface of 



