36 SPONTANEOUS GENERATION OF PLANTS 



well studied on high mountains, especially the Alps of Swit- 

 zerland, where besides, every modification of lasting ice and 

 snow is comprised within a narrow range that may be survey- 

 ed with comparative facility. 



From the foot of the glaciers to the highest tops of the 

 mountains, the ice and snow present a constant change of stra- 

 tification and structure. Below, the strata average eight feet 

 in thickness, and the ice-crystals are often two inches in di- 

 ameter. On the summit of the glaciers the thickness of the 

 strata is at most two feet, and sometimes only six inches, and 

 the crystals having become gradually smaller on the limit of 

 the glacier, pass into that sort of granulated snow which in 

 Switzerland is called Firn. The appearance of this fim marks 

 the limit of a very important change in the meteorological 

 conditions. Whilst the height at which the glaciers begin, 

 as well as the line of perpetual snow, varies in Switzerland 

 fi'om 6,000 to 10,000 feet, according to the exposure, thefirn- 

 line, at about 8,000 feet, appears to be comparatively inde- 

 pendent of temperature. At the height of from 10,000 to 

 12,000 feet above the sea, M. Hugi sometimes observed a heat 

 of from +15° to H-20° R. (the thermometer being probably 

 exposed to the direct rays of the sun), but no melting of the 

 snow, as is remarked below the firn-line at much lower tem- 

 peratures; (see Hugi's Naturhistorische Alpenreise). At such 

 high temperatures M. Hugi saw the fresh-falling snow losing 

 its needles or rays, and converting itself into grains, so as to 

 constitute Jlrn, whilst the old firn became loosened to the 

 depth of several feet, so as to resemble a heap of hemp-seed. 



The Palmella nivalis is found exclusively on the fim, be- 

 ginning at the firn-line and ending about 1,000 feet above it. 

 It is never seen either on a glacier or common snow ; its fa- 

 vourite habitat being sunny slopes where the snow is quickly 

 changed into firn. In August it is already blackish and de- 

 caying at the firn-line, in full growth at 8,200 feet, and just 

 springing at 9,000 feet. It is interesting to find that not on- 

 ly is the existence of the plant strictly dependent on that of 

 fim, but that the form of the former bears an evident relation 

 to the structure of the latter. The little plant, in its nascent 

 state, has the form of the letter Y, the simple radicle descend- 

 ing between two grains of the second layer, and the two little 

 branches embracing one grain of the surface-layer of the firn. 

 In its incipient state it tinges the firn with a delicate rose co- 

 lour, which is not observable when the eye is brought to the 

 same level as the surface of the fim ; but when fully develop- 

 ed, the plant appears above the surface of the firn,*^ which is 

 then beautifully crimson-coloured. The Palmella afterwards 



