THE AXGIOSPERMAE 



1325 



Fig. 1239. — Rhinanthns angustifoUiis (alpiniis). A, Vertical section of flower. The dotted 

 line shows the route from the upper corolla opening to the nectary. B, Flower from front. 

 Above, the butterfly door, open; below, the humble bee door, shut but often forced open 

 by the bees. C, R. major (hirsutiis). Front view of upper lip, with both doors open. 

 (After MuUer-Lippstadt. ) 



and movable and the pollen is shaken out of them by contact with the 

 insect, while a fringe of hairs on the anthers prevents the pollen from 

 scattering. 



{e) Wasp Flowers 



Many flowers may be visited by wasps as well as by bees and the identity 

 of the pollinator seems to depend upon the district. For example, in certain 

 parts of Europe Symphoricarpus racemosus is chiefly pollinated by wasps, 

 whereas in other areas its pollinator is usually the Hive Bee, although wasps 

 may occasionally visit the flowers. Such flowers can scarcely be regarded 

 as true wasp flowers and the number of flowers which are normally and 

 almost exclusively pollinated by wasps is quite small. True wasp flowers are 

 not very conspicuous, the prevailing corolla colour is reddish-brown, which 

 contrasts somewhat with the yellow anthers, but this colour may be more 

 conspicuous to wasps than it is to human beings. One of the most common 

 wasp flowers is Scrophidaria nodosa; indeed all the members of the genus 

 which have been studied appear to rely upon wasps for their pollination. 

 The dull purple flowers of the orchid, Helleborine, are also constantly fre- 

 quented by wasps, the nectar being easily accessible. 



In S. nodosa, which we may take as a type (Fig. 1240), the flowers are 

 quite small and are arranged in dichasial cymes, which are often incomplete. 



