BEES WHICH VISIT ONLY ONE KIND OF FLOWER 



flight synchronous, or nearly so, with the period of inflorescence 

 of the plant to which they restricted their visits. This theory 

 offers an explanation of the rise of oligotropism by the observa- 

 tion of existing conditions. There may be, and often are, acces- 

 sory factors, as small size, time of flight, length of flight, weak 

 flight, vicinity of nests, and the number of bees. 



The relation of the domestic bee to various flowers affords 

 an ever-present illustration of the way in which the oligotropic 

 habit might arise in the case of a bee wifh a short term of flight. 

 While the basswood and white clover are in bloom the honey- 

 bee visits these flowers almost exclusively. Again, in the fall 

 in Maine it confines its attention solely to the goldenrods. 

 In California at times it collects nectar exclusively from the 

 sages; in Michigan from the willow-herb, and in other regions 

 from other plants. If from any one of these plants it also ob- 

 tained its supply of pollen and was on the wing only while it 

 was in bloom, it would be a monotropic bee in the strict sense 

 of the word. There is here no question of competition; the 

 bees come to procure the great abundance of nectar, and pollen 

 is gathered at the same time as a matter of convenience. But 

 where a bee flies from early spring to late fall and requires a 

 large amount of stores, it is evident that it can never become 

 oligotropic. 



There can be no competition where there is an overabundance 

 of supplies. No other early blooming flowers yield so much 

 pollen and nectar as the willows. No other genus of honey- 

 plants in early spring is so valuable to the apiarist as Salix. 

 Honey-bees gather large quantities of pollen, and in some 

 localities are reported as storing from 8 to 15 pounds of honey 

 per hive from this source alone. Four species of Andrena, 

 which are on the wing for about a month, visit the willows ex- 

 clusively, because during their comparatively short term of 

 flight they can readily obtain all the pollen and nectar they re- 



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