356 THE BIOLOGY OF FLOWERING PLANTS 



insects of modern orders were well represented, nearly all, 

 however, with biting jaws. In the tertiary epoch, where 

 the angiosperms predominate, and representatives of many 

 modern families occur, almost all the modern types of 

 insects existed. The Lepidoptera and Hymen optera arose 

 with the angiosperm flora, and the one is unthinkable 

 without the other. 



Floral Classes. — Many details of floral structure can be 

 brought into relation with the structure and habits of par- 

 ticular insects, and with the way in which they visit the flower. 

 Partly according to structure, and partly according to their 

 insect visitors, Miiller divided the entomophilous flowers 

 into nine classes : — 



Po, Pollen flowers, without nectar, but with a super- 

 abundant production of pollen which is gathered for food, 

 especially by bees. Examples are the poppy, the roses, 

 and the rock-roses. In some flowers special " food pollen " 

 which has lost, partially or completely, the power of germina- 

 tion, is formed in special stamens, as in Cassia. 



A, Flowers with exposed nectar, such as the Umbelli- 

 ferae, many Saxifragaceae, the maples, the elder, the lime. 

 The flowers are often small, wide open, and with abundant 

 nectar. They are chiefly visited by short-tongued flies, 

 ichneumons, and beetles, though the maples and lime are 

 visited by bees. 



AB, Flowers with partly concealed nectar, such as the 

 buttercups, many Cruciferae, the willows. The nectar is 

 partly concealed in short corolla tubes, by hairs, or by scales, 

 but can be easily reached by dipterous flies and short- 

 tongued bees. 



B, Flowers with fully concealed nectar, such as the 

 eyebright, thyme, mint, whortleberries, heaths, forget-me- 

 nots. In these the nectar lies at the bottom of a fairly long 

 tube, and is accessible only to insects with fairly long tongues 

 — bees, butterflies, moths, hover-flies. It will be noted 

 that in this class are included for the first time typical 

 zygomorphic flowers, a form which allows of regulation of 

 the mode of visit. 



