PENTSTEMON GLABER. 65 



such flowers in the normal fashion and Halictus pulzenus likewise gave no 

 evidence of being disturbed by the change. 



PENTSTEMON GLABER. 

 NORMAL POLLINATION. 

 Habit and structure. — The plants of this species usually grow in small 

 communities on warm gravel-slides. The stems are about a foot high, 

 several in number and ascending. The flowers are arranged in brilliant 

 secund clusters. This is one of the large-flowered species, with not only a 

 comparatively large corolla mouth, but also a tube of nearly the same size. 

 Hence, its nectar is the most accessible of all the species of this genus in the 

 region. The staminode is broadly spatulate and covered for nearly half 

 its length with long hairs in two rows. The flowers are protandrous, the 

 anthers on the longer filaments maturing first and arching above the entrance 

 to the corolla mouth. The young stigma is straight, extending forward 

 just behind the front pair of anthers. When the stigmas become receptive, 

 the four anthers are nearly through dehiscing and the style elongates, its 

 tip arching sharply downward between the front pair of anthers and almost 

 touching the staminode. In older flowers the staminode coils inward, 

 coming in contact with the stigmas (plates 12 and 17). 



Behavior. — Osmia phaceliae works persistently at the tip of the bud, 

 trying to gain entrance to the corolla. When the flower is about ready to 

 bloom, the bee succeeds in opening it. In mature flowers it stands at the corolla 

 entrance and scratches the dorsal surface of its thorax on the anthers, 

 and then goes into the corolla-tube and secures nectar. Osmia pentstemonis 

 lands where the lobes of the lower lip bend downward ; it usually comes for 

 pollen and enters the flower to the point where the anthers brush against the 

 thorax. The latter is first well rubbed on the front pair of anthers and then 

 on the rear ones. Its dorsal surface rubs back and forth against the anthers 

 until the stigmas as well as the scopa become white with pollen. It rarely 

 if ever seeks both pollen and nectar, but some individuals pass the anthers 

 and take nectar only. Osmia melanotricha collects pollen in the same manner, 

 ignoring the nectar, in spite of the fact that the corolla-tube is nowhere so 

 narrow that it could not obtain this with its short tongue. Osmia densa 

 is so large that its body fills the entire corolla, the tip of the abdomen reaching 

 to the corolla mouth. It comes for nectar and the under surface of its 

 abdomen rubs the staminode while it is sipping. In more mature flowers 

 with a curved style, the stigma brushes closely against its back. In seeking 

 nectar, Osmia coloradella lands on the lower petals and stands upright, 

 bringing about pollination by contact with its dorsal surface. 



Vespa germanica stands at the angle of the corolla mouth and rubs the 

 thorax against the anthers so hard that a scratching sound is heard, while it 

 moves back and forth 5 to 10 times during the process. The hairs on its head 

 touch the anthers and stigma as it sucks nectar. Just before leaving the 

 flower, it stands at the edge of the corolla mouth and with the front legs 

 scrapes off and eats the pollen that has fallen on its head. Andrena madro- 

 nitens goes into the flowers upside down and collects pollen only, while A. 

 vicina enters for nectar alone and remains for a long time at each flower. 



