ON THE VERTICAL RANGE OF ALPINE PLANTS. 255 
On the Vertical e Plants in the Caucasus, By 
Dr. Gustav Raps, of Tiflis. 
(Communicated by Sir Joszru Hookzn, K.C.S.L, F.R.S., F.L.S., and 
translated by the Senior Secretary of the Linnean Society.) 
[Read June 19th, 1890.] 
I wore by the present communication to induce ardent moun- 
taineers, especially the English, who have of late years chosen the 
Caueasus as the scene of their perilous excursions, to render 
valuable service to Science. It is much to be desired that 
climbers should not neglect organic living forms in the upper 
alpine zones of this country, and that they should particularly 
observe those sporadic forms which occur here and there in the 
domain of perpetual ice and snow. It may certainly sound 
strange to speak of Phanerogams living above the snow-line, but 
it is nevertheless a fact. Above the snow-line there exist small, 
restricted areas of exceptional climatic character, from which the 
snow is either absent, or from which, notwithstanding their 
elevated position, it vanishes during the summer. These localities 
are either bare ridges, ribs, or precipitous rocky walls, or else 
they consist of chaotic heaps of stones, mostly volcanic, which 
have rolled down from the eircumjacent expanses of ice and 
névé. 
The refractive action of the rays of light and heat on such 
places is altogether different from that on ice and snow surfaces, 
and these stones possess besides an extraordinary faculty for 
absorbing heat. To take an instance, the porous weathered 
dusky trachyte, and the frequently occurring blistery, blackish 
lava greedily absorb the direct rays of the sun, while the sur- 
rounding eoherent ice and snow strongly reflect them. In the 
height of summer, and towards its close, from the beginning of 
August to the middle of September, when the atmospheric 
conditions of the Armenian highlands are favourable in respect 
of dryness and clearness of sky, then the heat of the sun exerts 
unusual power. The spots mentioned as occurring ın the regions 
of perpetual snow, not only become warmer themselves during 
the day, but at night also they give out a certain warmth ; and it 
is to this economy of heat must be ascribed the fact that certain 
LINN. JOURN.-—BOTANY, VOL. XXVIII. x 
