Bramble-bees and Others 



pears under the requisite conditions. In Its 

 natural state, the plant with the mighty hol- 

 low cylinders Is of no possible use to the 

 Osmia, who knows nothing of the art of per- 

 forating a woody wall. The gallery of an 

 Internode has to be wide open before the In- 

 sect can take possession of it. Also, the clean- 

 cut stump must be horizontal, otherwise the 

 rain would soften the fragile edifice of clay 

 and soon lay it low; also, the stump must not 

 be lying on the ground and must be kept at 

 some distance from the dampness of the soil. 

 We see therefore that, without the intervention 

 of man. Involuntary in the vast majority of 

 cases and deliberate only on the experimenter's 

 part, the Osmia would hardly ever find a 

 reed-stump suited to the Installation of her 

 family. It Is to her a casual acquisition, a 

 home unknown to her race before men took 

 it Into their heads to cut reeds and make them 

 into hurdles for drying figs In the sun. 



How did the work of man's prunlng-knife 

 bring about the abandonment of the natural 

 lodging? How was the spiral staircase of 

 the Snail-shell replaced by the cylindrical gal- 

 lery of the reed? Was the change from one 

 kind of house to another effected by gradual 



2o6 



