172 BRITISH PLANTS 



into three classes, based upon the availability of the 

 honey : 



1. Those with freely-exposed honey, which may be 

 visited by all kinds of insects, even those with the shortest 

 tongues (flies, beetles, short-tongued bees, wasps) — e.g., 

 saxifrages, gahum, ivy, most of the Umbelliferse, bar- 

 berry, hedge - mustard, spindle-tree. Many of these 

 flowers are small, but their conspicuousness is increased 

 by the massing of them together (see paragraph on in- 

 florescences, p. 178), or they make their presence evident 

 by a strong scent. Short-tongued insects are not efficient 

 pollinators, because they seldom confine their attention 

 to one species of flower. Such flowers are also more 



Fig. 72. — Christmas Rose (HeUeborus). 



1, longitudinal section of flower: a, honey-leaf; 6, carpels; c, stamens; 

 d, sepals ; e, receptacle. 2, honey-loaf, enlarged. 



exposed than others to insects which rob them of honey, 

 but are useless in effecting pollination. They are also 

 liable to have their honey spoiled by rain. 



2. Flowers with half-concealed honey. These are, 

 evolutionaUy, flowers of a higher type than Class 1. 

 Their honey lies deeper, and is more difficult to get at. 

 It is more protected from rain, and is less exposed to the 

 ravages of unwelcome guests — e.g., buttercup, stonecrop, 

 many Crucifers, potentil, etc. Th^re is every gradation 

 between the flowers of this class and the preceding. The 

 insects have tongues between 2 and 3 lines long (a line 

 is Y? inch). They are mostly short-tongued bees and 

 the longer-tongued flies. Among the unbidden guests of 

 flowers are the wingless and crawling insects — e.g., ants. 

 They enter the flower on foot, but before the honey is 

 reached the path is often stopped by viscid secretions on 



