PENTSTEMON. 



113 



Experiments. — These dealt largely with single and mixed bouquets, 

 though both natural and plant-bouquet competition were also concerned. 



There were no visitors to the P. secundiflorus flowers when that bouquet 

 was placed 6 inches from the P. gracilis plants. However, when these 

 flowers were mixed in the same cluster, Osmia went from P. gracilis to P. 

 secundiflorus and behaved in the same way at both species. It probably 

 visited P. secundiflorus in this case without noticing that it had gone to a 

 different flower. Although the corolla mouth of the P. secundiflorus flower 

 is very large, Halictus went into it upside down just as in P. gracilis. 



Summary. — In the competition with separate boquets, Pentstemon 

 halli and gracilis were about twice as attractive as glaber, owing to the pref- 

 erence shown by Osmia and Prosopis. P. barbatus again received no visits, 

 while the ratio between P. glaber and P. unilateralis was 24 : 19, this similarity 

 being suggested by the resemblance of the flowers. The extra-regional 



