r 



FLOWERS AND INSECTS. XX 



EVOLUTION OF ENTOMOPHILOUS FLOWERS 



Charles Robertson 



In his Fertilisation of flowers (pp. 594, 595) Muller arrives at the 

 following conclusions with regard to the development of flowers: 



The transition from wind fertilization to insect fertilization, and the first 

 traces of adaptation to insects, could only be due to the influence of quite 

 short-lipped insects with feebly developed color-sense. The most primitive 

 flowers are therefore for the most part (except, for instance, Salix) simple, 

 widely open, regular, devoid of honey or with their honey unconcealed and 

 easily accessible, and white or yellow in color (for example, most Umbelliferae 

 and Alsineae, many Ranunculaceae and Rosaceae) . 



Gradually, from the miscellaneous lot of flower-visiting insects, all much 

 alike in their tastes, there arose others more skilful and intelligent, with longer 

 tongues and acuter color-sense; and they gradually caused the production of 

 flowers with more varied colors, honey invisible to or beyond the reach of the less 

 intelligent short-tongued guests, and various contrivances for lodging, pro- 

 tecting, and pointing out the honey. 



The Ichneumonidae at first surpassed all other visitors in observation and 

 discernment, and they were thus able to produce inconspicuous flowers which 

 escaped the notice of other visitors. On the appearance of sand wasps and 

 bees these inconspicuous flowers were banished by competition to the less 

 frequented localities (for example, Lister a to shady woods). 



The sand wasps (Sphegidae) apparently took the place to a great extent of 

 the ichneumons, and produced flowers where organs had to be thrust apart 

 (Papilionaceae) , or where a narrow cavity had to be entered (Labiatae), or 

 where some other action similar to the act of digging had to be performed. 

 Subsequently bees seem to have entered on joint possession of most of these 

 flowers, and to have added special adaptations of their own. 



The true wasps (Vespidae) could establish themselves by the fear of their 

 sting (and of their jaws) in sole possession of certain flowers with wide open 

 mouths and abundant honey. These they developed further in relation to 

 their wants (Scrophtdari-a, Symphoricarpos, Epipactis latijolia, Lonicera alpi- 

 gena) ; but where wasps are scarce the flowers are utilized by other insects. 



Bees (Apidae), as the most skilful and diligent visitors, have played the 

 chief part in the evolution of flowers; we owe to them the most numerous, 

 most varied, and most specialized forms. 



307] 



[Botanical Gazette, vol. 63 



