ROBERTSON— FLOWERS * INSECTS UMBELLIFER-(E. 453 



Heracleuvi lanatum, Mx. — This plant bears large umbels of white flow- 

 ers. Well developed plants have 2 or 3 secondary umbels and sometimes 

 one of the third order. Five umbels of each order bore an average of flow- 

 ers and umbellets as follows : 



ist order — • o male and 420 hermaphrodite flowers in 19 umbellets. 

 2d order — 120 " " 303 " " " 20 " 



3d order — 389 " " 46 " '• " 20 '' 



As a rule, the primary umbel is entirely hermaphrodite, and umbels 

 of the third order are entirely male. A single umbel (primary), borne 

 on a weak plant, produced 160 male and 94 hermaphrodite flowers in 14 

 umbellets. The opposite of what occurs in Zizia ana Poiytcsnia, the pro- 

 portion of hermaphrodite flowers decreases from the primary umbel. The 

 hejmaphrodite flowers are proterandrous. 



This is the first plant to show Larrida; and Sphecidse. On account of 

 the exposed situation of the nectar, we find a diminution in the propor- 

 tion of bees and an increase in Parasitica, Crabronidae, and especially of 

 diptera. I found more flies on Heracleum than on any other umbellifer 

 except Pastinaca. But Pastinaca shows only 7 more flies in a much larger 

 list. Heracleum is especially rich in .Syrphidae, showing 21 species in a 

 list of 174 visitors, while Pastinaca shows only 22 species in a list of 275. 

 The list is also rich in Crabronidse, especially species of Crabro- Cicuta 

 shows an equal number, Crabro being partly replaced by Oxybelus. 



Pimfinella integerritna, Benth. & Hook. — This agrees in a general 

 way with Zizia and Polytsenia, and should be compared with them. Five 

 umbels of each order produced an average of flowers and umbellets as 

 follows : 



1st order — 409 male and o hermaphrodite flowers in 14 umbellets. 

 2d order — 174 " " 72 " " " 14 " 



3d order— 35 - " 47 " " •' 9 



A primary umbel on a plant bearing only i umbel produced 36 her- 

 maphrodite flowers, with many male ones, in 17 umbellets. The herma- 

 phrodite flowers are proterogynous. 



Eulophus Americafius^ Nutt. — The flowers are white. Five umbels of 

 each order- produced an average of flowers and umbellets as follows : 



1st order — 25 male and 1S2 hermaphrodite flowers in 13 umbellets. 

 2d order — 159 "' " 13 " ' " 12 " 



3d order — 51 •' '• o " " " 7 " 



Commonly, umbels of 1st order contain only hermaphrodite flowers, 

 those of the 2d order only male flowers. Umbels of the 3d order are rare 

 and entirely male. The hermaphrodite flowers are proterandrous. 



From their early blooming and fully exposed nectar, Eulophus and 

 Heracleum show the greatest proportion of flies. Eulophus shows 52 flies 

 in a list of 97. Tiedmannia, which is exposed to a richer hymenopterous 

 fauna, shows 52 flies in a list of 156. 



