28 



NORMAL AND EXPERIMENTAL POLLINATION. 



The most significant variation was that of Apis, indicating the possible 

 fluctuations from day to day, but similar differences of less degree are to 

 be noted for practically every species. 



The visitors noted at the same time of day, 8 h 30 m to 9 h 30 m a.m., at the 

 same location, with 65 open flowers in bloom and under observation in 

 each case, are shown in table 7. The first list represents the visitors at 

 about the middle of the flowering season and the second those at the end. 

 There were no plants of Rubus deliciosus in bloom lower down in the canyon 

 at the time the second list of visitors was made. 



Apis and Halictus, the two most important pollinators of the middle of 

 the flowering period, were almost completely absent at the end, but the 

 situation was exactly reversed for Bombus and Prosopis. On the contrary, 

 Andrena maintained its number throughout, though the three species showed 

 as many types of distribution. 



Table 8. — Visitors to adjacent areas on different days. 



Reciprocal checks at the two stations showed that the differences recorded 

 were due to location and not to time. Since they were situated in the same 

 canyon and but 150 meters apart, it is probable that the contrast between 

 the numbers for Apis and those for Bombus, Andrena, and Osmia is to be 

 ascribed to the difference in the associates of Rubus in the two places. 

 In station 1 it was grouped with Prunus demissa and P. pennsylvanica, 

 while at station 2 it was associated with Geranium especially. However, 

 it is quite possible that the difference was due to habit rather than to any 

 difference in conditions. 



