PENTSTEMON GRACILIS. 75 



found at Long's Ranch on the Ute Trail on June 19. The last four lists 

 were made in the vicinity of the Alpine Laboratory; 50 flowers were under 

 observation on the first two days, June 15 and 16; 85 open flowers on 169 

 spikes on the third, June 17; and 72 flowers on 175 spikes on the fourth, 

 June 18. 



EXPERIMENTS. 



CHANGE OF POSITION. 



Racemes inverted. — Bombus juxtus entered the inverted flowers as if 

 it did not notice the difference. It stayed in the corolla for a shorter time 

 than with normal flowers and probably did not find the nectar. Osmia 

 phaceliae pushed into the corolla, thrust out its ligule, and, not finding the 

 opening to the nectary, went to the next flower. It also failed to obtain 

 nectar here and then visited a third flower that was in the normal position. 

 The hairy thorax rubbed the mature pair of anthers, regardless of whether 

 this was the front or rear pair. It also visited flowers with the pollen 

 practically shed, the deflexed stigma scraping the thorax as the bee sipped 

 nectar. 0. pentstemonis ate the pollen that had fallen on the floor of 

 the corolla, as also that on the staminode and anthers. Prosopis varifrons 

 turned upside down in order to gain entrance to the flowers. 



Racenie horizontal. — Bombus juxtus turned to take a horizontal 

 position and entered at once in the usual relation to the parts. 



MUTILATION. 



Landing-platform removed. — The lower lip of the corolla was removed 

 to destroy the landing-platform and in consequence Bombus and Apis were 

 not able to enter such flowers. Osmia phaceliae did not need the lower lip 

 for support, but straddled the staminode in such a position as to take nectar. 



Brush of staminode removed. — There was no difference in the behavior 

 of the visitors to these flowers. 



Anthers and recurved portion of upper lip removed.— Halictus 

 pulzenus entered the flowers upside down in the usual way and rubbed the 

 upper surface of its body against the filaments, as if noting no change. 



Upper lip partly removed. — This exposes the anthers to full view, but 

 leaves the lower lip unchanged as a landing-platform. It also gives the 

 observer a much better opportunity to view the interior of the flower while 

 the bee is securing nectar. As Clisodon terminalis sucks nectar, it moves 

 its head back and forth once or twice and the upper parts become covered 

 with pollen, which is then removed by the stigma in older flowers. In the 

 case of Bombus juxtus, the first pair of anthers rub the top of the abdomen 

 and the second the top of the thorax, but only when mature. In these 

 flowers the bee did not go to the exposed nectary directly, but always passed 

 under the arch made by the stamens and style, as is its custom in normal 

 flowers. When the style is mature, it is in position to touch the back of the 

 abdomen. 



Lobes of upper lip separated. — Osmia phaceliae goes into these flowers 

 apparently without noticing any difference, the whole procedure being 



