882 



LIMITS OF DISTRIBUTION. 



distribution are dependent at the present day on climatic conditions; the manner in 

 which the species has come to occupy that area has not been determined by the 

 existing climate, but by geological processes which have always been the cause of 

 the migrations of plants on a large scale. It also becomes a question in each 

 individual case to what extent under past and present conditions the means of 

 plant-dispersion would have free play. 



The different areas of distribution vary greatly in size. Many species are only 

 encountered on a single mountain, or in a particular valley, or on one island, as the 

 case may be. These are called endemic species. As examples of such endemic 

 species from the regions of Southern and Central Europe we may mention the 

 following: Iberis Gibraltarica (Gibraltar), Uuzomodendron Burgceanum (Central 

 Spain), Dioscorea Pyrenaica (Central and Eastern Pyrenees), Saxifraga florulenta 

 (Liguria and Piedmont), Saponaria lutea (South-western Alps), Heracleum alpinum 

 (the Jura), Hieracium Grisebachii (the Oetzthal in the Central Alps of Tyrol), 

 Daphne petrcea (Val Vestino), Rhizobotrya alpina (Fassa and Belluno), Gentiana 

 Frolichii (Carniola and Carinthia), Wulfenia Garinthiaca (Carinthia), Sempervivum 

 Pittonii (Serpentine mountains in Upper Styria), Schiverekia Podolica (Podolia), 

 Viscaria nivalis (Rodna Gebirge, in Northern Transylvania), Pedicularis limnogena 

 (Bihar Mountains), Hepatica Transsylvanica (Southern Transylvania), Hdberlea 

 Rfiodopensis (Rhodope Mountains in Roumelia), JanJccea Heldreichii (Thessalian 

 Olympus), Helichrysum virgineum (Mount Athos), Campanula Aizoon (Mount 

 Parnassus), Hypericum fragile (Euboea), Globularia stygia (Mount Khelmos), 

 Genista Melia (Melos), Cephalanthera cucullata (Crete), Centaurea crassifolia 

 (Malta), Petagnia saniculifolia (Sicily), Lereschia Thomasii (Calabria), Batatas 

 sinuata (Ischia), Helichrysum frigidum (Mountains of Corsica). 



The species contrasting with the endemic as regards distribution, i.e. those whose 

 range extends over almost the whole of the plant-inhabited earth, are called cosmo- 

 politan. Their number is very small. 



Only in the case of endemic species occupying an extremely restricted area do 

 we sometimes find the plants evenly distributed over the whole area. They are 

 more usually scattered unequally over the district in question. The spots where 

 they grow in large numbers close together are separated by tracts where they do not 

 grow at all, but where other species have taken possession of the soil, and the line 

 f distribution then incloses separate habitats which are often at a considerable 

 from each other. In such cases we speak of the area of distribution as 

 How far this depends on properties of the soil has been explained on 

 00, and we need here only add that in mountainous or hilly countries 

 degree and direction of the inclination of the ground may have an important 

 fluence. Owing to the fact that a slope receives very different amounts of light 

 *t accordiDg as it faces north or south, different parts of a single mountain 

 nbit diverges in respect of temperature and moisture as great as exist on 

 ad between p aces separated by a degree of latitude. Also the differences 

 -r cond^ons between slopes facing east and west respectively, and 



