1917] 



ROBERTSON— FLOWERS AND INSECTS 



309 



Putting speculation aside, 

 'iect will be limited to the s 



the further consideration of this 



and the behavior of the insects which we know. Social flowers are 

 those which are so closely approximated that the visitors may 

 readily pass from one to another without taking wing or climbing. 

 They are usually found in heads, spikes, or close umbels. The 

 simplest flowers which we know are non-social flowers of class AB, 

 flowers with partly concealed nectar. Insect visits to them 

 show : 



Class AB . . 

 Visits 



Individuals 



Species 



41 



o 



Bees 



56.8 



43-7 

 70.2 



Diptera 



31.2 

 32.8 

 20.4 



Other 



Hymen 



optera 



4 7 



19 5 



8.0 



Lepidop- 





4.8 



2.7 

 0.7 



Coleoptera 



Hemip- 



tera 



2-3 

 I . 2 



o-5 



Total 



866 



405 

 H38 



These are evidently bee flowers, although they are not exclu- 

 sively visited by bees. No insects except bees prefer flowers of this 

 kind. There are no non-social flowers of class AB which are 

 adapted to miscellaneous insects or to particular kinds of visitors 

 except bees. On 14 species of class AB bees showed 43. 7 per cent 



* 



of the visits and 70. 2 per cent of the individuals. Of course it is 

 possible that the primitive non-social flowers of class AB were 

 visited by a miscellaneous set of the least specialized anthophilous 

 insects. If so, the short-tongued bees must have tended early to 

 monopolize them, while the other insects paid more attention to the 

 forms which became social. 



Observations of 221 visits to 17 non-social flowers of class A, 

 flowers with exposed nectar, show: bees 33.4, Diptera 45.7, other 



men 



14.4, Coleoptera 



Hemiptera 6.3. Here the 



Diptera predominate, and the group is rather miscellaneous. 

 Some of the group are distinct fly-flowers (Asimina triloba); some 



im). The 



are quite simple {Asimina, M\ 



lophyll 



dark color and pendulous position of Asimina are hardly typical. 



Caulopkyll 



None of 



these are simple like ordinary non-social flowers of class AB. 

 Most non-social A have epigvnous nectaries {Hypoxis, Circaea, 



