UNBIDDEN GUESTS 275 



of smell, and not by sight. When the insect begins 

 to get near the flower, then the colours attract its 

 eyes, and often " honey guides" (p. 161) are furnished 

 by the plant to help it to find the entrance. 



Protections against Unbidden Guests. 



We have seen how certain flowers are specialised 

 for certain types of insects, and we are now in a 

 position to appreciate the safeguards possessed by 

 many Alpines, whereby insects or unbidden guests, 

 which can perform no service to the flower by acting 

 as cross-pollinators, are warned off* or excluded. 

 Some plants, not so well adapted to meet this 

 difficulty, are frequently robbed of their honey or 

 pollen, by insects which are not likely to visit another 

 flower of the same species. 



Unbidden guests are of two classes : those 

 which approach the flower on the wing, and those 

 which crawl up from below by means of the flower- 

 stalk. The former are excluded, as we have seen, by 

 the concealment of the honey, or by the special shape 

 of the flowers, which precludes their entrance, or by 

 the closure of the throat of the flower by special 

 means such as scales, or by the presence of tufts of 

 hairs or bristles inside the flower, which prevent 

 some insects penetrating as far as the honey. In 

 certain species, such as the Martagon Lily (p. 259) 

 and Lychnis vespertina (p. 165), which are adapted 

 for fertilisation by night-flying Lepidoptera, the plants 



