THE ANGIOSPERMAE 1257 



great " Natural History of Plants ", much of it based upon original observa- 

 tion. The astonishing discoveries by von Frisch of the organization of nectar 

 or pollen collection by the honey bees, belong rather to Entomology than to 

 Botany, in spite of their obvious bearing on pollination. They have now 

 been expounded in more than one popular work in English. 



Bees visit flowers either to collect nectar or pollen for the food stores 

 of their hives, on which their broods must depend during the winter, while 

 less social insects pay their visits for the same ends, but consume their finds 

 on the spot. But were these the primitive attractions? Diels thought not 

 and pointed out that many insects at the present day bite or suck juice from 

 the tissues of flowers either where no nectar is formed or else is inaccessible 

 to them. He suggests that the first insect visitors to the flowers of the 

 earliest Angiosperms were probably beetles, the principal order of insects 

 in Jurassic times, which came to eat the tissues, as beetles now eat the 

 staminodes of N\mphaea, Victoria, Calycanthus and Eupomatia, at the same 

 time bringing about pollination. The beetles were probably the only im- 

 portant group of flower-visiting insects before the Tertiary period and it is 

 significant that at least one Cycad, Encephalartos, is pollinated by a beetle 

 which lays its eggs in the ovules. Many are thereby destroyed, but the rest 

 are effectively pollinated. 



Diels calls beetle-pollination cantharophily. Although few, if any, 

 flowers now rely exclusively upon beetles, they are sufficiently common 

 visitors to have at least a secondary importance in many species. Recently 

 an interesting relic fauna of beetles has been found to be exclusively asso- 

 ciated with the giant Lobelias in central Africa. Both the plants and the 

 insects are survivors of vanished forest conditions and it may well be that a 

 mutual dependence has been established. 



The line between false nectaries or juicy outgrowths which may be 

 eaten or sucked and the nectaries which secrete actively, is not a hard and 

 fast one. Some of the false nectaries contain sugary sap and on the other 

 hand some structures which have all the appearance of nectaries are devoid 

 of secretion. (See also under Nectaries, p. 1251.) Once nectar secretion was 

 established in flowers its overwhelming attraction for a variety of animals 

 would ensure that it survived and spread. Its appearance was one of the 

 momentous steps in plant evolution, comparable in importance to the 

 evolution of the seed. 



At the present day nectar is the chief cause of the frequentation of 

 flowers by insects, exceeding even pollen as an attraction. Its attractiveness 

 varies, however, considerably, with regard to both its quantity and quality. 

 The quantity produced is affected not only by internal factors but also by 

 the weather, by the season, and by the time of day. In the early morning 

 there may be little nectar present and the bees may visit flowers for pollen 

 only, which later in the day they will visit for nectar. On the other hand, 

 Fagopvrum, the Buckwheat, produces its dark-coloured nectar only in the 

 mornings and is not visited by bees in the afternoon. Fagopynim nectar is 

 attractive to bees, but each flower contains very little. A bee visits about 



