50 .JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
which flourish most abundantly in one particular zone, although they 
may sometimes ascend or descend to that above or below. 
On the otlier hand, while we are able to distinguish between three 
such zones, it is not possible to definitely define their limits, and this for 
many reasons. If we determine the mean average limits of a sub-alpine 
plant in one locality, and compare them with the limits of the same plant 
in another district, we are almost sure to find a considerable discrepancy, 
owing perhaps to the more favourable situation in regard to aspect, soil, 
water, &c., of the former over the latter, or vice versa. Then, again, 
many plants which are essentially lowland species, such as Caltha 
yalustris, L., or Campanula rotundifolia, L., ascend to high elevations in 
the Alps, and are not more characteristic of one zone than of another 
in Switzerland. As, however, such plants are among the commonest in 
the plains of Central and Northern Europe, there can be no doubt as to 
their lowland origin. The so-called upper limit of alpines is a good 
illustration of how impossible it is to define these zones. Until a few 
years ago, it was commonly stated that the upper limit of the alpine 
zone was the line of perpetual snow. As a matter of fact, alpine species 
will flourish at any altitude in the Alps, provided they can obtain a 
minimum of soil in a situation free from snow for a few weeks in the 
summer. For instance, in one of the tributaries of the Mer de Glace, 
near Chamonix, there is, as is well known, a rock called the Jardin, at a 
height of about 9,000 ft. above sea-level. On this oasis in a wilderness 
of perpetual snow and ice alpine flowers bloom in August, when for a 
short period the rock is free from snow. All other vegetation has ceased 
quite 2,000 ft. below. In other places alpines have been gathered at still 
greater altitudes — at 12,000 ft. or more. 
Although it is not possible to accurately define the limits of the alpine 
and sub- alpine zones, one is generally able to determine whether one is 
dealing with one or other of these zones by observing the presence of 
characteristic sub-alpine or alpine species. In Switzerland the suh- 
alpine zone is especially characterised by the presence of Vaccinium 
Vitis idcsa, L., Melampyrum sylvaticum, L., Prenanthes piurjmrea, L., 
Lonicera alpigena, L., L. nigra, L., and others. The alpine zone is dis- 
tinguished by the occurrence of Rhododendron ferrugineum, L., B. hirsu- 
tum, L,, Pmus Cemhra, L., Salix herbacea, L., >S'. reticulata, L., and 
many species of Anemone, Primula, Androsace, &c. 
In studying the flora of any district the knowledge of the elevation 
at which one is working is often useful in determining the zone. The 
altitude of any locaHty can be readily ascertained by reference to 
maps, &c. The following may be taken as the rough limits of the various 
zones in Switzerland : * 
Lowland, 0 to 3,500 feet. 
Sub-alpine, 3,500 to 5,000 feet. 
Alpine, above 5,000 feet. 
It must, however, be remembered that these limits vary in the different 
* The following centres are within the alpine zone : Zermatt, Saas, Arolla, Zinal, 
Davos, Upper Engadine, Pontresina, Murren, Belalp, &c. Grindelwald and Chamonix 
are sub-alpine. 
