GERANIUM CAESPITOSUM. 39 



roses thus treated receiving a relatively large number of visitors. The 

 difference between the two, however, was almost wholly a consequence of 

 the preference of Bombus proximus for the honey-flowers of the rose. The 

 addition of various odors to flowers of the rose regularly decreased the 

 number of visitors about half, quite irrespective of whether the odor was 

 one ordinarily regarded as pleasant. It seems evident that this decrease 

 was due to the strange odor disturbing the habitual response of the pol- 

 linators. 



GERANIUM CAESPITOSUM. 

 NORMAL POLLINATION. 

 Habit and structure. — The flowers of Geranium are regular and the 

 five nectaries are so placed that the nectar in all is equally exposed and 

 accessible. All the visitors except Halictus sp. usually come for nectar. 

 The inner row of anthers dehisce first, followed by the outer row from 

 10 to 24 hours later (plate 7). 



Behavior. — Bombus juxtus lands on the disk-shaped corolla and proceeds 

 to circle the stamen group, taking nectar at each of the nectaries. It 

 secures nectar from flowers in which all the anthers have dropped off, 

 indicating that the flow continues while the stigmatic surface is receptive. 

 A few individuals are satisfied to suck nectar from only one or two nectaries 

 at each flower, and B. bifarius usually stops likewise at only a few of those 

 in each flower, instead of making the complete round. Halictus pulzenus 

 comes for both nectar and pollen. It visits each of the 5 nectaries, some- 

 times going around the circle twice in succession. After getting all the 

 nectar available, it walks up the anthers, scrapes out pollen with its front 

 legs, and packs it on the hind ones. This bee is so small that it can stand 

 under the outwardly curved anthers. When in this position, pollen falls 

 on its back, but it touches the stigma only as it flies away. Halictus was 

 seen to pick up the pollen that had fallen on the corolla, brush its head well 

 with the front legs, and then eat the pollen. Prosopis elliptica has a shiny 

 body on which pollen does not collect easily. It is so small that in dipping 

 into the nectaries only the lower shorter row of anthers or the recurved 

 styles touch its abdomen. This species is probably not a very effective 

 pollinator on this account. 



Andrena madronitens is a pollen collector. It hangs suspended from the 

 styles and filaments, and moves around them repeatedly, gathering pollen. 

 It collects with its mouth and front legs and places the pollen on the hind 

 ones. Monumetha albifrons lands with its head pointing toward the nec- 

 taries. It tips its abdomen upward as it goes from nectary to nectary, and 

 this gives it the appearance of standing on its head. The tip of its abdomen 

 rubs the anthers as it sucks nectar. A pis mellifica stops at all the nectaries 

 and makes no effort to get pollen. The thoracic hairs become covered with 

 the latter and scrape the anthers and style, dusting them with pollen as it 

 moves about the nectar circle. Osmia bruneri and Sphex vulgaris also visit 

 each nectary, where they appear to be standing on their heads. The head 

 of the latter is hairy and serves to collect and deposit pollen. Pseudomasaris 

 vespoides likewise goes to each nectary, the dorsal surface of the bee touching 

 the anthers in one flower and the stigmas in the next. 



