13 10 A TEXTBOOK OF THEORETICAL BOTANY 



Shelter from Wind 



The shape of the flower or its associated organs may often provide pro- 

 tection to visiting insects against wind or cold. Many small insects seek 

 shelter in the flowers and inflorescences of certain plants. The gall 

 wasps, which are responsible for fertilization of the Fig, afford a good 

 example which will be referred to later (p. 1327). Many small flies obtain 

 protection within the spathes of Aroids and during their sojourn there per- 

 form pollination. This mechanism will be discussed on p. 2017. Apart, 

 however, from these highly specialized examples, flowers with large corollas, 

 especially when not joined into a narrow tube, do provide shelter either from 

 wind by day or cold by night. Beetles are often found in the flowers of 

 species of Magnolia and ants have been observed resting in the flowers of 

 Tropaeohnn and Trollius. Various small insects shelter in the capitula of 

 Compositae which close at night. To what extent these insects contribute 

 to pollination is, however, doubtful. 



Edible Pollen 



Although the majority of insect-pollinated flowers offer their visitors 

 nectar or sweet sap, there are some flowers which provide pollen. Such 

 flowers are often types with regular, radially symmetrical corollas and the 

 pollen is fully exposed. Some of these flowers, e.g.. Anemone, open early in 

 the year when insects are short of food. Bees use considerable quantities of 

 pollen to nourish their young and in early spring probably collect more 

 pollen than nectar. Such flowers produce great quantities of pollen and 

 consequently can well afford to spare a large proportion of the pollen they 

 produce to provide food for the visitors, in return for the essential service of 

 pollination. Pollen is not always edible and only a comparatively small 

 number of plant pollens are used for food by insects. Many are largely 

 ignored, while certain pollens (6'.^^., Aesciilus) are definitely poisonous to bees. 



Before commencing a description of entomophilous pollination mech- 

 anisms we may outline the classification of the Insects as follows: 



1. Hymenoptera Bees, Wasps, Ichneumon Flies, Ants. 



2. Lepidoptera Butterflies, Moths. 



3. Diptera Hover Flies, Two-winged Flies. 



4. Coleoptera Beetles. 



5. Thysanoptera Thrips. 



6. Hemiptera Bugs. 



7. Neuroptera Dragon Flies, May Flies. 



8. Orthoptera Earwigs, Grasshoppers, Locusts, Crickets. 



These eight orders of insects have been arranged in series according to 

 their importance as pollinators. The last two orders, which geologically are 

 probably the most ancient, play no part in any pollination mechanism so far 

 as is known. 



The main types of entomophilous pollination have already been enum- 

 erated on p. 1282. 



