452 TRANS. ST. LOUIS ACAD. SCIENCE. 



of bees is larger than in any other species in the table. Compared with 

 Erigenia, this is owing to concealment of nectar and to the presence of a 

 more numerous bee-fauna. Compared with Eryngium, which has more 

 deeply-seated honey, it is owing to a smaller number of competitors, re- 

 sulting from early blooming. The proportion of bees to other hymenop- 

 tera is reduced by the appearance of lower forms. The proportion of 

 diptera is reduced by concealment of nectar. 



Polytcenta Nuttalltt\ DC. — This plant agrees with Zizia aurea in color, 

 proterogyny, time of blooming, mode of nectar concealment, and in the 

 general character of its visitors. Five umbels of each order produced an 

 average of flowers and umbellets as follows : 



1st order — 335 male and 9 hermaphrodite flowers in 14 umbellets. 

 2d order — 275 " " 120 " " " iS " 



3d order — 48 " " 55 " " "11 •' 



The primary umbel is, as a rule, entirely male, the proportion of her- 

 maphrodite flowers increasing in the secondary and tertiary umbels. On 

 a plant bearing umbels of the 4th order, the primary and all of the second- 

 ary umbels bore only male flowers; an umbel of the 3d order bore 384 

 male and 74 hermaphrodite flowers in 18 umbellets; one of the 4th order 

 bore 63 male and 54 hermaphrodite flowers in 12 umbellets. 



Osinorrhiza longistyh's, DC. — Five umbels of each order bore an av- 

 erage of flowers and umbellets as follows; 



1st order — 58 male and 27 hermaphrodite flowers in 6 umbellets. 

 2d order — 47 " "18 " " " 6 " 



3d order— 38 " " 15 " " " 5 '' 



4th order — 29 " •' 11 " " '" 5 " 



The hermaphrodite flowers are proterandrous, and the proportion of 

 male flowers remains about the same in umbels of all orders. The flow- 

 ers are white. The nectar is fully exposed, and, as a consequence, the 

 number of diptera equals the number of hymenoptera. 



Saiiicula Marilatidica, L. — The umbels contain i to 4 hermaphrodite 

 flowers surrounded by from 20 to 70 male flowers. The styles of the her- 

 maphrodite flowers are strongly exserted from the start, and, although 

 without receptive stigmas at first, the stigmas develop before dehiscence, 

 so that the flower is proterogynous. When the stamens become dehis- 

 cent, the styles are strongly recurved, holding the stigmas down against 

 the sides of the ovary. Sometimes the petals hold an anther so firmly 

 between them that it is not released until it has lost its pollen. 



S. europsa has the styles exserted at first, but Schulz* regards it as 

 proterandrous. 



The petals are incurved so that they cover the disc, making the nectar 

 less accessible to the shortest tongue. Accordingly, the list shows more 

 hymenoptera than diptera. Although the heads are by no means showy, 

 a rich supply of nectar insures an abundance of industrious visitors. 



