54 NORMAL AND EXPERIMENTAL POLLINATION. 



for hour periods from 9 h 35 m to ll h 35 m in the morning and the next two for 

 an hour period from 2 to 4 in the afternoon. 



Both visitors and visits were slightly though not significantly greater 

 to the scented flowers. The grand totals for the different odors are much 

 alike, except in the case of almond. While visited least in the first experi- 

 ment, its total was 2 to 4 times greater than for the others. 



SUMMARY. 



The inversion of the flower resulted in about half of the visits being 

 fruitless at first, but later both inverted and horizontal flowers received 

 many more visits than the normal. Mutilated flowers in general were about 

 half as attractive as normal ones, but they differed greatly among them- 

 selves. The removal of the corolla reduced visits from a half to a fourth, 

 in spite of the marked habit of Bombus in visiting Chamaenerium flowers 

 in order from the bottom upwards. On the other hand the removal of all 

 flower parts except the ovary and the nectary increased the visits 5 times 

 over the normal, doubtless because the nectar was more fragrant and 

 accessible, thus permitting the bees to work more rapidly. Artificial 

 flowers of paper were often inspected, but they received only a single visit, 

 in spite of the addition of honey. Painted ones were about half as attractive 

 as normal flowers, suggesting that the neglect of artificial flowers was due to 

 small differences in form and texture, since the colors were unnatural in 

 both cases. Blue was the preferred color, but not decisively so. Honey 

 did not attract greater numbers of bees, while scented powders almost 

 eliminated visits, the number of inspections equaling the visits to normal 

 flowers. The number of visitors was the same for blossoms perfumed with 

 other flower odors and normal ones, but the visits were about half as many 

 to the former. Flavoring extracts seemed to increase attraction slightly, 

 but the significant fact was the marked effect of almond in augmenting the 

 number of visitors. 



PACHYLOPHUS CAESPITOSUS. 



NORMAL POLLINATION. 



Habit and structure. — This species possesses the largest and most 

 fragrant flowers of any in the region. It is white in color the first evening, 

 becoming pink the next morning. When the calyx 

 is normal, the flowers open between 5 and 7 in the 

 evening and the process usually requires but 2 to 7 

 minutes, the unfolding of the petals being so rapid 

 that the movement is easily seen. The style and 

 stamens are covered with very small black diptera 

 when the flower opens. At this time the anthers are 

 dehiscing and the stigmas are receptive. The under 

 surface of the stigma lobes is covered with pollen, but 

 the receptive surface is free from it. The tube of 

 the calyx is about 10 cm. long and is filled with nectar 

 for more than half its length at the time of opening 

 (plate 9). The amount of nectar varies considerably, 

 as is shown by its weight in several flowers. These were picked at 7 



