CHAr. X. QUANTITY OF POLLEN. 407 



outside of a flower is rarely utilised as a means for 

 cross-fertilisation by the aid of insects ; but this is the 

 case with several species of Euphorbia and with the 

 bracteae of the Marcgraviacese, as the late Dr. Cruger 

 informed me from actual observation in the West 

 Indies, and as Delpino inferred with much acuteness 

 from the relative position of the several parts of their 

 flowers.* Mr. Farrer has also shown f that the flowers 

 of Coronilla are curiously modified, so that bees may 

 fertilise them whilst sucking the fluid secreted from 

 the outside of the calyx. With one of Malpighiacese, 

 bees gnaw the glands on the calyx, and in doing so 

 get their abdomens dusted with pollen, which they 

 carry to other flowers.J It further appears probable 

 from the observations of Rev. W. A. Leighton, that the 

 fluid so abundantly secreted by glands on the phyllodia 

 of the Australian Acacia magnifica, which stand near 

 the flowers, is connected with their fertilisation^ 



The amount of pollen produced by anemophilous 

 plants, and the distance to which it is often trans- 

 ported by the wind, are both surprisingly great. Mr. 

 Hassall found, as before stated, that the weight of 

 pollen produced by a single plant of the bulrush 



* 'Ult. Osservaz. Dicogamia,' contained in the intercellular 



1868-69, p. 188. spaces. I further suggested, in 



+ 'Nature,' 1874, p. 169. the case of some other orchids 



% As described by Fritz Miiller which do not secrete nectar, that 



in 'Nature,' Nov. 1877, p. 28. insects gnawed the labellum ; and 



'Annals and Mag. of Nat. this suggestion lias since been 



Hist.' vol. xvi. 1865, p. 14. In proved true. H. Miiller and Del- 



niy work on the ' Fertilisation of pino have now shown that some 



Orchids,' and in a paper subse- other plants have thickened pe- 



quently published in the ' Annals tals which are sucked or gnawed 



and Mag. of Nat. History,' it has by insects, their fertilisation being 



been shown that although certain thus aided. All the known facts 



lcinds of orchids possess a nectary, on this head have been collected 



no nectar is actually secreted by by Delpino in his ' Ult. Osserv.' 



it ; but that insects penetrate the part ii. fasc. ii. 1875, pp. 59-63, 

 inner walls and suck the fluid 



