116 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 :— 
(az) Bee Fiowers proper (//). For rifling the nectar of these a proboscis of 
at most 7 mm. in length is necessary (e.g. Trifolium repens, Lotus). 
(2) Humsre-srz Frowrers (4%). For these a longer proboscis is required 
(e.g. Trifolium pratense, Aconitum). 
(c) Bez-Humsie-ser Frowrrs (4h). Calamintha alpina. 
(Z) Wasp Fiowers (Hw). Scrophularia nodosa. 
(e) Icunzumon Frowers (#7). Listera ovata. 
Owing to the great abundance of remarkable floral arrangements in Bre Flowers 
and HumsBie-BEE FLowrrs—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 Brz Frowrrs proper (//) (in which a proboscis of at most 
7mm. 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 officinalis Z., even for certain 
Muscidae. This last example may therefore be described 
as transitional between Flowers with concealed nectar and 
Bee Flowers. The Lepidoptera, 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. 
Fic. 26. Trifolium repens, L. HumBiE-BEE Frowers (///) (with nectar concealed at 
catarasie 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 
