II2 INTRODUCTION 
they visit (Knuth, ‘ Bliitenbesucher derselben Pflanzenart in verschiedenen Gegenden,’ 
I, pp. 14 and 15). 
Hermann Miiller arrived at conclusions similar to mine by collating his observa- 
tions on the visitors of alpine flowers with partly concealed nectar. In the Alps 
(‘Alpenblumen,’ p. 487), white flowers are chiefly influenced by Diptera, while yellow 
ones are equally visited by Diptera and short-tongued bees. 
According to Hermann Miiller (‘ Fertilisation,’ pp. 74-9 and 231-4; ‘ Weit. 
Beob., I, pp. 320, 321; IJ, pp. 241, 242), the yellow flower of Ranunculus and 
Potentilla are chiefly visited in central Germany by small bees belonging to the 
genera Andrena and Halictus—‘ These cross-pollinating agents correspond as com- 
pletely, in size and degree of adaptation, to the dimensions and adaptational stage 
of these flowers as if each were made for the other’ (‘Alpenblumen,’ p. 488). 
The blackish-purple flowers of this class are almost exclusively visited by flies, 
and in the Alps by Lepidoptera as well. The way in which they resemble decaying 
flesh in colour is, perhaps, what specially induces flies that are fond of decomposing 
substances to visit them. ; 
4. Flowers with concealed Nectar (C). 
This class, again, is connected with the previous one by numerous transitional 
forms. The nectar is always quite out of sight of visitors, being concealed in 
pouches, or by hairs or projecting floral parts, so that it remains invisible even 
Fic. 22. Flowers with concealed nectar. (1) Trollius europaeus Z. (2) Lycopuseuropaeus Z. 
(in outline). 2. Nectary. 
_ when the petals are fully expanded in the sunshine. Although actinomorphous 
forms still predominate (e.g. species of Pulsatilla, Trollius, species of Geranium, 
Erodium, Cardamine pratensis, Cakile maritima, Malva, Rubus, Oxalis, Epilobium, 
Ribes, Lythrum, Sempervivum, Polemonium, Myosotis, Vaccinium, Calluna, Pyrola, 
Symphoricarpos, Allium, and others), this class of flowers also includes many species 
exhibiting more or less well-marked zygomorphism, this indicating a higher degree 
of floral specialization (e.g. Veronica, Euphrasia, Scrophularia, Lycopus, Orchis, 
Thymus, Mentha, Origanum, and others). 
White and yellow, colours which predominated in the two first classes of nectar 
flowers, scarcely appear at all in flowers with completely concealed nectar, but give 
place to reds, blues, and violets. 
