OBSERVATIONS ON SOME PLANTS EXHIBITED. 



177 



along the Rocky Mountains and the Andes. Numerous species 

 of Gentian are also characteristic of the European Alps, tall 

 species as the medicinal G. lutea, four feet in height, being found 

 on the lower slopes, and G. glacialis, about one inch high, occur- 

 ring close to the perpetual snow. The Alpine Gentians are 

 represented in Britain by Gentiana nivalis, at an elevation of 

 2,400-3,300 feet, on the Clova and Breadalbane mountains of 

 Scotland, and G. vema of Westmoreland, &c, ascending to 

 2,400 feet. Other Alpine plants common to British mountains 

 and of Switzerland are species of Saxifraga, as Saxifraga ojjposi- 

 tifolia, &c. ; Dry as octopetala, Alchcmilla alpina, with silky 

 leaves, species of Lycojpodium, &c. ■ 



Prof. Henslow then explained how the same species are now 

 only found in widely separated countries, as Great Britain, 

 Pyrenees, Alps, Scandinavian Mountains, and in the Arctic 

 regions. After the' great Glacial epoch, when the climate of 

 North Europe, including the British Isles, resembled the present 

 condition of Greenland or Spitzbergen, the temperature became 

 less severe, and Arctic plants (which had been driven southwards 

 by the advancing ice and low temperature) were able to extend 

 their distribution. The climate, however, continued to become 

 more and more temperate ; and as the ice all disappeared from 

 our mountains the temperate flora spread westwards from the 

 continent, while the Arctic flora, dying out from the lowlands, 

 ascended, and became isolated upon the higher parts of the 

 mountains, where they now exist. The land subsequently sank — 

 where the German Ocean and the Channel now flow — and so the 

 British Isles were formed, being cut off from the mainland. 



Double Flowers.— Some double wood Anemones and furze 

 supplied material for a few observations on the process of 

 " doubling " as compared with the " symmetrical increase " of 

 parts, which has now become a hereditary feature in the 

 florist's Auriculas exhibited. In the former there is a conversion 

 of stamens and carpels into petals, with their subsequent multi- 

 plication. In the latter case some of, or all the whorls of the 

 flower are regularly increased in the number of their parts; so 

 that if five be the normal number, there may be whorls of sixes, 

 sevens, or even eights. On the other hand, by insufficiency, 

 instead of a superabundance of nourishment, the numbers might 

 be reduced to fours and threes, or even twos. Thus fours to sixes 



