Chapter III 



AREAS, THEIR CENTERS AND BOUNDARIES 



Area Concept Defined: — By area {area geographica) is understood, 

 taking the Latin meaning of this word, the region of distribution of any 

 taxonomic unit (species, genus, or family) of the plant (or animal) 

 world. A distinction is made between natural areas, occupied by a 

 plant as a result of its dispersal caused by the combined action of 

 various natural factors, and artificial areas, arising as a consequence of 

 the intentional or accidental introduction of a plant by man. 



Within the limits of its area a plant does not occupy the entire 

 surface of the earth but leaves smaller or larger intervening spaces 

 unoccupied. This is due to the biological pecuharities of plants and to 

 their adaptation to local habitat conditions, which even within the 



Fig. I. — Example of a discontinuous area. Areas of Saponaria ocymoides and S. pumila, 

 restricted to mountain-tops in the Alps. (After Hegi). 



limits of a small territory may vary to a considerable extent. Among 

 such local conditions are: physical and chemical properties of the soil 

 and its humidity, micro-relief, micro-climate, geographical location with 

 reference to the countries of the world, influence of animals and man, 

 interrelations with other plants, etc. The character of the distribution 

 of a plant within the hmits of its area or, in other words, the local 

 distribution of a plant, is known as its topography (de Candolle, 



1855)- 



The area of distribution of a plant is best pictured by maps, on 

 which all its known habitats are indicated by dots. Connecting by a 

 line all the outer points of the distribution of a given plant, we are able 

 to judge as to the shape of its area. The shape of an area depends 

 on the combined effect of the biological peculiarities of the plant and 



25 



