NECTAR 359 



D, Diptera flowers, visited chiefly by flies, and usually 

 less highly specialised than the last two classes. The small, 

 slightly zygomorphic flowers of the speedwells are visited 

 by syrphid flies which can reach the nectar in the very short 

 tubes. There are also cases of very peculiar specialisation. 

 In the cuckoo-pint, Arum maculatum, Hies are attracted to the 

 inflorescence, enclosed in its spathe, by the lurid red colour 

 and rather putrid odour of the terminal portion of the 

 spadix axis. When they have crawled in they are trapped 

 among the female flowers at the base of the inflorescence 

 by a ring of hair-Uke abortive stamens (Fig. 50). They 

 escape only when these have withered, and must pass up 

 through the male flowers, the anthers of which are now 

 dehiscing. The Aristolochias, which again have a reddish 

 colouring, also trap flies in a curiously shaped perianth. 



K, Small insect flowers, pollinated by small bees, flies, 

 and beetles often not more than 2 mm. long ; Her minium 

 monorchis is an example. 



Food of Visiting Insects. — The substantial advantage 

 which the insect derives from the visit to the flower is, in 

 almost all cases, a supply of food, typically nectar, sometimes 

 pollen. In some flowers neither is available ; in such 

 highly specialised flowers as some of our native orchids, 

 e.g. Orchis latijolia^ and Orchis morio, which are visited 

 by bees, there is no nectar, and the pollen, cemented in 

 poUinia, cannot be collected for food. The spurs are lined 

 with juicy cells the delicate walls of which are pierced by 

 the bee, which sucks the contents. Bees learn to pierce the 

 wall from the outside, thus obtaining the sap without carrying 

 off the poUinia, a habit that is also acquired in connection 

 with some nectar flowers like Erica Tetralix. In Pinguicula 

 alpina the nectarless spur is lined with special " fodder " 

 hairs which are filled with a sugary sap. Similar hairs 

 occur in Verbascum and in some orchids. 



Nectaries are probably derived from glands of the active 

 hydathode type, which, on leaves, excrete water and mineral 

 salts ; the presence of extra-floral nectaries on leaves has 

 already been mentioned. In the flower the nectary, 



