112 



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 ; II, pp. 241, 242), the yeUow flower of Ranunculus and 

 Potentilla are chiefly visited in central Germany by small bees belonging to the 

 genera Andrena and Hahctus ' 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 



Fig. 22. Flowers with concealed nectar, (i) Trollius europaeus L. (2) Lycopus]europaeus L. 



(in outline), n. 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. 



