94 



FERTILIZATION OF SPRING FLOWERS ON THE YORKSHIRE COAST, 



Helomyza. The circle widens as the days get warmer ; the humble- 

 bees become more numerous ; a few hybernated butterflies appear, 

 the earliest usually being Vanessa urtica3; ants and wasps appear ; 

 a long-tongued fly, Volucella, appears, and, in addition, other flies, 

 as PoUenia rudis, Phorbia, Siphona geniculata, and Dilophus albi- 

 pennis. These are the insects upon which the flowers have to 

 depend for their cross-fertilization, and this approximately the order 

 of their appearance. In Table I. I have tabulated my observations 

 for periods of seven or eight days, as convenient. The first five 

 columns give figures of all the insects (individuals) seen visiting 

 flowers in 1895, and the second five give the same for 1896. The 

 absolute numbers are, of course, much affected by the state of the 

 weather, the proportions to a less degree, for the habits of various 

 insects vary considerably : some, such as the butterflies, usually 

 fold their wings when a cloud-shadow passes over them ; while 

 others, like Thrips, are almost always to be found in flowers which 

 afi'ord them shelter. 



Observers hitherto have neglected to study the frequency of 

 insect-visitors, upon which the amount of cross-fertilization de- 

 pends, confining themselves to the mere consideration of the 

 variety of visitors attracted. To the entomologist such facts are 

 suSicient, but to the botanist the number of individuals is of quite 

 as great importance. 



A short review of the efficiency of these insects in flower- 

 fertilization may not be out of place. 



