118 ? INTRODUCTION 
Hermann Miiller supposes that these different colours were evolved as a result 
of the possession of and necessity for discriminative powers in bees, and it does not 
therefore appear wonderful that not only white, yellow, red, violet, blue, brown, and 
even blackish (Bartsia) are represented in the most varied degrees among Bee 
Flowers, but several colours may even appear on the same flower, as in Polygala 
Chamaebuxus, Viola tricolor, Cerinthe major, Galeopsis versicolor, Astragalus 
depressus and alpinus, and so on. 
A large number of yellow-flowered Papilionaceae (Genista, Sarothamnus, Coro- 
nilla vaginalis, Hippocrepis comosa) form the only exceptions. It would appear, 
according to Miiller, that the yellow colour has here been so strongly transmitted 
that ‘variations, which of course constitute the necessary condition for the production 
of different colours, may not have appeared at all.’ 
Various flowers of this class are visited and pollinated ed by a few species of 
humble-bees, or even by a single species. 
Fic. 28. Humble-bee Flowers with Nectar concealed particularly deeply. (1) Aconitum Lycoc- 
tonum Z. (in outline). (2) Corydalis solida Sy. (the corolla-tube has been bitten through by Bombus 
terrester). 
Aconitum Lycoctonum is of particular interest in this connection. The nectar 
of this flower is, hidden so deeply that only insects with an exceptionally long 
proboscis are able to reach it. 
Especially interesting is the fact that in central Germany this flower is visited 
exclusively by Bombus hortorum Z., and in the Alps exclusively by B. opulentus 
Gerst. 2. These two humble-bees possess a proboscis longer than that of any 
other species of the same genus living in the districts named. That of B. hortorum 
is 21mm. long, and that of B. opulentus 22mm. The latter species has hitherto 
been observed on no other flower. We have here, therefore, vzcarzous species. 
In Jamtland (in central Sweden) C. Aurivillius (Bot. Centralbl., xxix, 1887, 
pp. 125 and 126) frequently observed B. consobrinus Dah/d. acting as a pollinator, 
in addition to B. hortorum Z. Both species are ‘particularly well adapted to reach 
the nectar.’ We have here, then, a second vicarious species, characteristic of the 
‘northern alpine regions,’ or perhaps it is only a vicarious variety, for Schmiede- 
knecht (‘Apidae Europ.,’ pp. 295, 297, 305) describes the former as a race of the latter. 
Lastly, MacLeod has again met with B. hortorum Z. as a visitor of Aconitum 
