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 Flowers and Insects — Umbellifer.e.* 



By Charles Robertson. 



The Umbelliferae have remarkably uniform flowers, the nectar 

 being generally exposed, or at most only slightly concealed by the 

 incurved petals ; and, since they bloom in succession from early 

 spring to late autumn, are particularly w^ell suited for an in- 

 vestigation which aims to discover the effect of the time of bloom- 

 ing on the character of the visitors. It is obvious that a flower 

 must depend for visitors not only upon the fauna of the region in 

 which it grows, but upon the insects which are flying while it 

 blooms. t Accordingly, I have arranged the plants in the order 

 of blooming, or at least in the order in which they were observed. 

 This will enable us to consider the order in which they succeed 

 one another, their relations to the particular insect fauna upon 

 which they depend, and to the general insect fauna which reaches 

 its maximum of variety in the hot summer. We can compare a 

 plant with one blooming earlier or later, can discover peculiari- 

 ties in the lists which are due to time of blooming, and can elim- 

 inate this cause to ascertain the effect of difterence of structure. 



For aid in the determination of the bees I am indebted to Mr. 

 E. T. Cresson, of the flies to Dr. S. W. Williston, of the beetles 

 and bugs to Mr. C. A. Hart. The Chalcids, as far as made out, 

 were named for me by Mr. L. O. Howard. My collecting and 

 identification of the minute hymenopteraand diptera are very im- 

 perfect. The flowers with exposed nectar are very abundantly 

 visited by these forms, but to collect them requires special atten- 

 tion to them. Then, they have been so imperfectly studied, that 

 it is hard to determine them or to assort them accurately. 



* Compare especially Miiller: Fertilization of Flowers, Weitere Beobachtungen, and 

 Alpenblumen. AlsoSchulz: Beitrage zur Kentniss der Bestaiibungseinrichtungen und 

 der Geschlechtsvertheilung bei den Ptlanzen. 



f The importance of the time of blooming is especially emphasized by MacLeod : Sta- 

 tistiehe Beschouwingen omtrent de Bevruchting der Bloemen door de Insecten, Botanisch 

 Jaarboek, eerste jargang, 1889, Gent. 

 V.-3-8 



