224 A BOOK OF INSECTS 



stamens hav r e shed their pollen. The mountain crane's- 

 bill is almost in the same case, but not quite ; its stigmatic 

 lobes unfurl while some of the stamens remain upright, 

 and before they have shed all their pollen. Thus self- 

 pollination is possible as a last resort. In the dove's-foot 

 crane's-bill the pistil matures in advance of the second 

 whorl of stamens, and the flower is often self- fertilised ; 

 while in G. pusillum it matures before any of the stamens, 

 and self-fertilisation is the rule. These facts suggest, as 

 Lord Avebury has said, that " where we find within the 

 limits of one genus some species of flowers which are 

 much more conspicuous than others, we may suspect that 

 they are also more dependent upon the visits of insects." 

 The same observer also proved many years ago that bees, 

 at least, exercise a deliberate choice in the matter of 

 colour, and show a distinct preference for blues and 

 purples ; while every field naturalist is aware that most 

 other insects evince a special liking for a particular kind 

 of flower to the exclusion of other kinds. We may there- 

 fore liken the brightly coloured petals of flowers to adver- 

 tisements. They say to the insects : " Here is nectar — 

 here is pollen ; come and sample the good things that I 

 hold in keeping." Moreover, it is interesting to notice 

 that the conspicuous blotches or lines of colour upon the 

 petals of flowers generally converge about the opening 

 which gives access to the nectary. Such specialised 

 markings have been appropriately called " honey guides " ; 

 and it is significant that they are absent from the petals 

 of night-flowers — where, of course, they would not be 

 visible, and would therefore be superfluous. " I did not 

 realise the importance of these guiding marks " (writes 

 Lord Avebury) " until, by experiments on bees, I saw how 

 much time they lose if honey, which is put out for them, 

 is moved even slightly from its usual place." 



