45S TRANS. ST. LOUIS ACAD. SCIENCE. 



In Erigenia bulbosa, Chaerophjllum procumbens and Hydrocotjle um- 

 bellata I found only hermaphrodite flowers; all of the other species bear 

 male flowers as well. Male flowers are most abundant in the centre of 

 the umbels, in the centre of the umbellets, and on the side of the umbel- 

 lets which is nearest the centre of the umbel. It follows that hermaphro- 

 dite flowers are most abundant on the outside of the umbels, on the 

 outside of the umbellets, and on the side of the umbellets which is nearest 

 the outside of the umbel. In Sanicula. however, the hermaphrodite flow- 

 ers are central, and in Zizia the fruitful umbellets commonly have a sin- 

 gle, central hermaphrodite flower. 



Erigenia, Zizia, Thaspium, Polytaenia, Pimpinella, and Sanicula Ma- 

 rilandica, have the styles strongly exserted, and are abundantly visited 

 by insects before the anthers are dehiscent. From a careful examination 

 of the styles in all stages, I am satisfied that they are proterogynous. 

 With the exception of Erigenia, they have the nectar concealed by the in- 

 curved petals. In the character of their insect visitors, with the exception 

 of Eryngium, they are the most highly specialized of Umbelliferae. 



In the proterogynous species — Zizia, Thaspium, Polytoenia, and Pim- 

 pinella — the primary umbel commonly contains only male flowers to sup- 

 ply the first stage of the secondary umbels, and the proportion of her- 

 maphrodite flowers increases in umbels of the 2d and 3d orders. On the 

 other hand, the proterandrous species — Heracleum, Eulophus, Pastinaca, 

 Cicuta, Sium, and Tiedmannia — commonly have the primary umbels en- 

 tirely of hermaphrodite flowers, and the last umbels entirely male, to sup- 

 ply the pollen for the second stage of the preceding umbels. This differ- 

 ence in behavior goes to support the view that the plants mentioned in 

 the former group are really proterogynous. 



In well developed plants the first and last umbels thus tend to special- 

 ization; but when the flowers are reduced to a single primary umbel, as 

 in the plants mentioned under Heracleum and Pimpinella, this umbel 

 contains both male and hermaphrodite flowers. 



