138 Zoological Society : — 



by a plant during one season. It is objected tbat " the sum of useful 

 temperatures will be found scarcely reckonable for any species ; and 

 no ordinary tliermometrical records are fairly available, on account of 

 the variable rates and degrees required by the different species of 

 the same flora or country, and differently required by the same species 

 at their different stages of growth," — to say nothing of the relations of 

 temperature to dryness or humidity, which still further complicate 

 the subject. The established routine of annual mean temperature 

 is therefore adhered to in the ' Cybele,' not as being the truest, but 

 because it is the only test practically available at present. 



It will have been seen that, notwithstanding a comparatively 

 uniform climate and a surface which seldom rises to any considerable 

 elevation, the flora of Great Britain exhibits, on a small scale, all the 

 effects of longitude, latitude, elevation, climate, and even of isolation. 

 Considering the careful and judicious manner in which Mr. Watson 

 has collected and arranged his information, the ' Cybele Britannica ' 

 deserves to be most attentively studied by all who are interested in 

 the general questions of Geographical Botany. 



As a standard of comparison for local Floras, its value will be 

 admitted by every botanist who has made himself acquainted with 

 the varied contents of the present volume. 



PROCEEDINGS OF LEARNED SOCIETIES. 



ZOOLOGICAL SOCIETY. 



June 26, I860.— Mr. E. W. H. Holdsworth in the Chair. 



On some Hybrid Ducks. By Alfred Newton, M.A., 

 F.Z.S. 



The phaenomena of Hybridism are in themselves so interesting, 

 and at present so little understood, that I venture to call attention 

 to some examples illustrating the subject, which I now have the 

 honour of exhibiting to the Society, and to make some observations 

 thereon. 



The proverbial fidelity of Pigeons, when once mated, has been 

 found a matter of much convenience to at least one gentleman who 

 has studied the great question of the "Origin of Species," by en- 

 abling him to experimentalize, comparatively without ^ difficulty, on 

 the different races, breeds, or varieties which can be produced from 

 one common stock *. I would remark, on the other hand, that the 

 tendency, under certain circumstances, to polygamy which obtains 

 among many of the Ducks, combined with their natural salacity, is 

 such as to render that family, perhaps, the one of all others in which 

 experiments on hybridism can be the most easily tried. 



The frequent occurrence of hybrids among the AnatidcB has already 

 attracted the notice of ornithologists, and among them of one of the 



* C. Darwin, 'On the Origin of Species,' London, 1859, p. 42. 



