POLLEN LOADS. 



127 



Table 87. — Composition and weight of pollen loads— Continued. 



MONUMETHA ALBIFRONS. 



Discussion.— Of the total of 207 bees, 121 carried pure loads of pollen, 

 i. e., from a single species of flower, while 86 had mixed loads. Three-fourths 

 of the latter consisted of 2 species, and one-fourth of 3 species, a single load 

 containing as many as 4 species. Pollen grains of conifers are not considered 

 as constituting a mixture, since they were purely incidental. They may 

 have been taken with the pollen sought or picked up separately, but in no 

 case did they involve a visit to the species from which they originated. 

 With the exception of Halidus pulzenus, no species represented by 4 or 

 more individuals was perfectly constant in its choice of pollen. Apis 

 mellifica and Andrena crataegi were the most constant of these, Bombus 

 occidentalis and Anthophora simillima among the least so. The 4 genera 

 represented by 2 or more species gave the following ratios between pure 

 and mixed loads: Andrena 19:10, Bombus 50:36, Halidus 6:2, Megachile 

 12:10. Each of these contained species that were largely or entirely con- 

 stant on the one hand, and those that were 50 per cent or more inconstant 

 on the other. 



