ROSA ACICULARIS. 33 



No previous floral study of Rubus has been made in America, but several 

 European species have received much attention (Knuth, 1908:352). 



EXPERIMENTS. 



MUTILATION. 



Floral envelopes or stamens removed. — Apis mellifica started to 

 land at a flower with the stamens removed, but flew away. The nectar 

 was clearly visible, but the excision of the stamens changed the appearance 

 of the flowers so much that it seemed to frighten this bee. Andrena 

 madronitens worked at flowers with the calyx and corolla or stamens gone 

 as at normal flowers. Prosopis episcopalis stopped at one with the stamens 

 and corolla removed and worked as usual, while Osmia bruneri visited a 

 flower with the perianth gone. These results are opposed to those obtained 

 with Rubus deliciosus, but this is readily explained by the difference in 

 the size and visibility of the petals. In strigosus these are not only several 

 times smaller than in deliciosus, but their position further decreases their 

 attractiveness. 



ROSA ACICULARIS. 



NORMAL POLLINATION. 



Habit and structure. — The corolla of Rosa is pink in color and widely 

 expanded, forming a broad landing- platform and a bright disk of color, 

 evidently visible to insects from some distance. The stamens are numerous 

 and the pollen abundant. A mild sweet odor adds to the apparent attrac- 

 tiveness of the flower. 



Behavior. — Bombus edwardsi tumbles about the stamens very rapidly, 

 collecting pollen in the corbiculae, on the mouth-parts, and the hairs of 

 the abdomen. Pollen was gathered at Rubus deliciosus in much the same 

 manner, and this bee goes from Rosa to Rubus or the reverse without 

 showing a preference for either. It did not stop at flowers in which the 

 stamens and pistils were covered by the unfolding petals, but went on to 

 the next open flower. The anthers in Rosa are not mature when the petals 

 are unfolding and the bee has perhaps learned by experience that the pollen 

 is not available until the petals are broadly expanded. One individual of 

 Bombus flavifrons endeavored to open a half-expanded flower, landing on 

 the lower petal and trying to push its head in, but after making several 

 unsuccessful attempts it flew away. B. bifarius tramples back and forth 

 among the stamens collecting pollen, the tip of its abdomen at the same time 

 rubbing the stigmatic surfaces and depositing pollen previously collected. 

 B. proximus collects pollen on the rose; it files low above flowers which are 

 opening but lands only on those with dehiscing anthers. 



Andrena crataegi collects pollen most industriously, even visiting flowers 

 with petals gone and stamens brown, trying to get pollen from the withered 

 anthers. Andrena vicina tramples rapidly over the stamen mass, going 

 round and round with its head buried among the anthers. The first two 

 pairs of legs gather pollen and pack it on the third pair. A. madronitens 

 arches the tip of its abdomen downwards toward its head, inclosing a 

 group of stamens. While in this position, it collects pollen rapidly with 



