THE ANGIOSPERMAE 



1259 



Origanum v id gore 

 Erodium cicutarium 

 Salix spp. 

 Onobrychis sativa 

 Taraxacum officinale 

 Stellaria media 



76% 

 65% 



0/ 

 /o 



0/ 



55 

 51 

 50% 



Trifolium repens 

 Melilotus alba 

 Persica vulgaris 

 Liriodendrun tulipifera 

 Pyrus communis (about) 



41% 

 36% 

 30% 



20* 



/o 



4/0 



All the above concentrations are subject to considerable changes, 

 especially if the nectar is exposed. For example, in Epilobium angustifoliiim 

 with exposed nectar, the concentration varies between 60 per cent, at a 

 relative humidity of 30 and 19 per cent, at a relative humidity of 79. 



The following figures show how the concentration varies with the time 

 of day, in the Plum, at the University of California Agricultural Station at 

 Davis, California, on ist March. 



Time 

 7-8 a.m. 

 9.40 a.m. 

 2.00 p.m. 



2.50 p.m. 



Concentration 



Temperature Rel. Humidity 



0/ 



/o 



8-1 

 25-8% 

 24-1% 



52-o°F. 

 59-o'F. 



7o-5°F. 

 I 



100 



0/ 

 /o 



/ 



o°F. 



85% 

 55% 



53% 



The Hive Bee, considered as a community, is polytropic, that is to say 

 that a variety of flowers are visited by members of one hive during the season. 

 The individual bee is oligotropic or may even be monotropic if the flying 

 season is short. When there is a long flying season successive broods will 

 work different species of flowers, with different flowering seasons. No 

 species of flower is adapted only to the Hive Bees. The great stores of honey 

 needed demand a wide range of visits and specialization would be a great 

 hindrance. Its medium length of tongue is best suited to open flowers or 

 those with only short tubes, while long-tubed flowers such as Digitalis, 

 Antirrhinum, Gladiolus, or Pentstemon are pollinated by Humble Bees, to 

 whose visits they are better suited. 



Even a small difference in the length of the floral tube may be a serious 

 barrier, as is shown by the Clovers. The tongue of the Honey Bee averages 

 6 mm. in length, that of Humble Bees varies between 7-5 and 20 mm. 

 The tube of the Red Clover flower averages 9 mm. in length. It is therefore 

 much frequented and pollinated by Humble Bees, although in dry seasons 

 its flowers may become short enough for the tongues of Honey Bees (see 

 also p. 1322). The White Clover, on the other hand, with a 6 mm. corolla 

 tube, is one of the favourites of the Honey Bee and one of its most important 

 sources of honey. There is a famous anecdote of Charles Darwin's which 

 relates the production of Red Clover seed to the number of cats in the 

 neighbourhood The cats control the number of field mice and the field 

 mice control the number of Humble Bees available for pollination. It 

 has been cynically added that the number of cats depends on the number 

 of maiden ladies. 



