GERANIUM CAESPITOSUM. 



41 



In the columns for July 16, 40 flowers were under observation for the two 

 successive hour periods. On July 25, only 26 flowers were in the group 

 observed during an hour period. 



As would be expected, the records for two successive hours resemble 

 each other closely, but depart much more widely from that made a number 

 of days later. This record contains but three of the species present on 

 July 16, and the number of visitors and visits is very low. The inversion 

 of the number for Bombus bifarius and juxtus is the most striking feature of 

 the two successive records. In table 23 the most important fact is the 

 change of dominance from Prosopis at the opening of the flowering period 

 to Bombus and Halictus near the close. This is to be explained by the 

 fact that the latter were working on preferred species earlier and went to 

 Geranium in abundance only when their choice became more restricted. 

 This is likewise the explanation of the doubling of the average number of 

 visitors per hour period in the later observations. 



EXPERIMENTS. 



CHANGE OF POSITION. 



Flowers vertical or inverted. — When the face of the flower was turned 

 so that it was vertical, Bombus juxtus found no difficulty in hanging on, 

 and its behavior was practically the same as at a normal flower. In the 

 case of inverted flowers, however, it experienced much trouble in keeping a 

 foothold. One individual landed on the bottom of the flower, which was 

 then uppermost, went over the edge to the face, but finally flew away with- 

 out securing nectar. Another went to an inverted flower that was half- open, 

 but did not succeed in opening it. It next went to another half-open 

 inverted flower, landing on the calyx and looking for the opening to the 

 nectaries among the sepals, and departed unsuccessful. 



MUTILATION. 



Cotton over nectaries. — A circle of cotton was placed at the base of the 

 filaments so that it covered the opening to the nectaries. One individual 

 of Prosopis varifrons flew around above the flowers without landing. Another 

 individual alighted and poked around the edges of the cotton, but did not 

 find the nectaries. A fly also landed and pushed out its ligule, but was 

 unable to locate the nectar. Bombus juxtus secured nectar from 7 flowers 

 by pushing aside the edge of the cotton until the nectary was exposed. 



Table 24. — Visitors to normal and mutilated floivers. 



