ii6 



INTRODUCTION 



of such flowers, it may happen that pollination can only be regularly effected by 

 a few species of bee. To this class of flowers belong the Papilionaceae, most of 

 the Violaceae, many Labiatae, Scrophulariaceae, the species of Aconitum and 

 Delphinium, and Corydalis solida, cava, fabacea, and others ; also Scrophularia nodosa, 

 Lonicera alpigena, Listera ovata. 



They fall into five groups : — 



{a) Bee Flowers proper {Hb). For rifling the nectar of these a proboscis of 

 at most 7 mm. in length is necessary (e.g. Trifolium repens, Lotus). 



(3) Humble-bee Flowers (Hh). For these a longer proboscis is required 

 (e.g. Trifolium pratense, Aconitum). 



{c) Bee-Humble-bee Flowers (^Hbh). Calamintha alpina. 



{d) Wasp Flowers [Hw). Scrophularia nodosa. 



{e) Ichneumon Flowers {Hi). Listera ovata. 



Owing to the great abundance of remarkable floral arrangements in Bee Flowers 

 and Humble-bee Flowers — such as the explosive mechanism in Sarothamnus, Genista, 

 and Ulex, the lever mechanism of Salvia, the spring mechanism of Medicago, and so on, 

 only a few can be indicated here by means of figures. For a detailed account of 

 such floral arrangements reference must be made to the second volume of this work. 



The visitors of Bee Flowers proper {Hb) (in which a proboscis of at most 

 7 mm. in length is necessary to secure the nectar) include, beside honey-bees and 

 long-tongued bees (with some of the parasitic humble- 

 bees), a few short-tongued bees, for the slight depth at 

 which the nectar is concealed allows them to reach it in 

 the regular way, and so to liberate the mechanism for 

 pollination. The same holds true for some Syrphidae, 

 and, in the case of Euphrasia ofiicinalis Z., even for certain 

 Muscidae. This last example may therefore be described 

 as transitional between Flowers with concealed nectar and 

 Bee Flowers. The Lepidoplera, on the other hand, are 

 probably never able to effect pollination : their long 

 proboscis permits them indeed to suck honey even from 

 bee flowers, but it is far too slender to set the floral 

 mechanism in motion. They are here, therefore, nothing 

 but nectar-thieves. The remaining visitors are only 

 occasional and accidental, and most of them are of no 

 use to the flowers. 



Humble-bee Flowers {Hh) (with nectar concealed at 

 a depth of more than 7 mm.) are almost exclusively 

 pollinated by humble-bees and other long-tongued bees. 

 In certain species, e. g. Erica Tetralix, Lepidoptera and Hover-flies seem to be able 

 to effect pollination when they visit the flowers. Bees with a relatively short 

 proboscis appear only as pollen-thieves, or else steal the nectar, by biting a hole 

 through part of the corolla, and thrusting their proboscis through it. In Germany, 

 for instance, Bombus terrester Z. does this to Trifolium pratense, Corydalis 

 solida and cava, and Lamium album. Honey-bees also frequently steal nectar 



Fig. 26. Xrifoliwm refiens, L. 

 A Bee Flower. 



