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 
2,400-8,800 feet, on the Clova and Breadalbane mountains of 
Scotland, and G. verna of Westmoreland, &c., ascending to 
2,400 feet. Other Alpine plants common to British mountains 
and of Switzerland are species of Saxifraga, as Saxifraga opposi- 
tifolia, &c.; Dry as octopetala, Alchemilla alpina, with silky 
leaves, species of Lycopodium , &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 
