THE BRITISH AND SWISS ALIMNI^ I'LORAS 
57 
many lowland plants, such as Cunipanulu. rohindij'olia, L., ascend to con- 
siderable elevations in the mountains. Such species must obviously be 
able to adapt themselves to great changes in climatic conditions. The 
reason why other species are confined to the lowlands is in part due to 
the want of this power of becoming acclimatised to different environ- 
ments. In order to more fully understand the phenomenon which we 
term acclimatisation, we must look closely into the factors which govern 
the environment. Schimper,* in his splendid work on plant geography 
considered from a physiological standpoint, puts forward six factors which 
govern the distribution of plants. They are : moisture, temperature, 
light, atmospheric pressure and wind, soil, and the fauna. All these 
conditions are very different in the Alps as compared with Britain, the 
intensity of illumination and the extremes of temperature being greater 
and the atmospheric pressure less. A species growing in an exposed 
situation in the Alps has to adapt itself to these conditions, otherwise 
it would perish. In so doing it may become specialised in constitution 
and in habit. Such a plant if transferred to our plains would stand a 
poor chance of adapting itself to our climate. For want, perhaps, of 
the intense illumination to which it had become adapted it dies, or, at 
the most, exists for a time. In short, it has become over-specialised, and 
has lost that elasticity of constitution which was necessary to overcome 
the change of climate. Thus it perishes where another plant less 
specialised will not only survive but flourish. 
Such may perhaps be a provisional explanation of how it is that 
many alpines can be grown in our rock-gardens. It must, however, be 
remembered that we are still on the threshold of our knowledge respect- 
ing the modifications induced in the constitution of plants due to 
climatic conditions, or change of conditions. Until we know more of the 
specialisation of types under these influences, we shall not be able to 
understand fiilly many of the phenomena met with in the cultivation of 
alpines. 
The question of the acclimatisation of plants is one of great importance 
when we seek to explain the origin of alpine floras. The origin of the 
alpine flora of Southern Europe is a subject which has been much 
debated, but the problem may be said to be still unsolved. The Alps, 
like most of our British mountains, are of comparatively recent geologic al 
date. The great lateral thrusts which formed the chief mountain ranges 
of Europe took place in Tertiary times, i.e. long after the deposition of 
the Chalk. " 
The formation of the Alps need not, however, be considered here in 
detail, for we are more especially concerned with an event of later date, 
known as the Glacial period. The Great Ice Age, as this epoch is often 
termed, took place at the close of Tertiary times, and is the most recent of 
all the great geological events in the earth's history with which we are 
acquainted. All the attempts which have been made to explain the 
origin of the Swiss alpine flora have attached great importance to the 
influence of this period of cold and ice on the flora which was then exist- 
ing in Europe, and also as having in the main determined the present 
distribution of European plants. 
* Schimper, A. F. W., Pflanzen-Geograpliie, 1898. 
