PENTSTEMON GLABER. 71 



flew away as if aware of the change. Another individual went into 3 of 

 these flowers and inserted its ligule into the nectary, but left without taking 

 nectar (plate 17). 



Corolla lips separated and staminode raised. — In flowers of this 

 type, Osmia phaceliae tried repeatedly to get on the lower lip of the corolla, 

 but slipped off. Finally it landed and then bumped into the staminode. 

 After doing this twice it went in at the side and obtained nectar. In 

 normal flowers 0. melanotricha has the habit of rubbing its back against the 

 anthers, but in these it failed to find them, and went instead to the nectary. 



Upper lip removed at the throat. — Osmia bruneri landed as usual 

 and secured nectar, the style touching its back in the process. 



Lower lip shortened half. — The lower lip constitutes the landing- 

 platform, and this experiment was devised to find out the response of visitors 

 when it was removed. Clisodon terminalis went into a flower without noting 

 the change; it then flew to a normal flower, and afterward to one with the 

 corolla mouth obstructed with cotton. When it did not succeed in entering 

 this, it flew away. Vespa germanica sipped some nectar, but did not stay 

 the usual time. Osmia phaceliae landed on the staminode, finding difficulty 

 in balancing itself, but finally made its way along the staminode until it 

 obtained a better foothold on the corolla-tube and was able to reach the 

 nectar. 



Lower lip removed. — Osmia melanotricha entered these flowers by 

 straddling the staminode and was able to secure nectar. 



Lower lip and part of tube removed. — The lobes of the lower lip 

 were removed, as well as the tube for a distance of 4 mm. Osmia bruneri 

 succeeded in landing after repeated attempts by taking hold of the anthers 

 with the front legs, turning upside down, and walking a short distance into 

 the flower; it then turned right side up with the front legs on the remaining 

 part of the lower lip. This gave it a sufficient foothold for gathering nectar. 



Lips removed except lower lobe. — The median lobe thus left formed 

 a landing-platform, so that Osmia phaceliae was able to obtain nectar in 

 the usual fashion. 



Corolla tube shortened half. — Clisodon terminalis poised in the air 

 before these flowers, but did not land. Melissodes fremonti, Osmia phaceliae, 

 and Andrena vicina entered them and obtained nectar. Some individuals 

 of Pseudomasaris vespoides landed, but could not hang on and suck nectar, 

 as too little of the corolla was left to serve as a platform for them. 



Petals separated. — When the petals are separated to the base, they 

 are long, slender, and recurved, since they lack mutual support. The 

 stamens consequently spread out in all directions. Osmia phaceliae went 

 directly to the nectar, instead of first standing at the corolla mouth and 

 rubbing its thorax, as in the normal flower. 



Lower lip split into three petals. — Osmia bruneri stood on the middle 

 petal and continued to suck nectar, in spite of the fact that its weight 

 caused this to bend down vertically. It did not come in contact with the 

 anthers and style at all in these flowers. 



