Chapter V 



TYPES OF AREAS 



The areas of species of plants are as diverse as the distribution 

 of plants is varied. It is, consequently, impossible to group all this 

 diversity into a definite number of types. Any hard and fast system 

 of classifying areas would be artificial, since it would not reflect the 

 natural diversity of plant distribution. Nevertheless, a definite ter- 

 minology for designating different types of areas is necessary. At- 

 tempts to elaborate such a terminology have been made by various 

 investigators. We give below two examples. 



According to Pachosky (1921, p. 209), the following types of areas 

 may be distinguished: (i) two races or two closely allied species may 

 inhabit one and the same region, i.e., may grow side by side — a coex- 

 tensive area; if the area of one such species is smaller than that of the 

 other, the smaller is called an included area (Bush, 1917); (2) two 

 species may inhabit different regions, in which case their areas are 

 either separate or contiguous; (3) the areas of two species, at the 

 point of contact, may overlap — an overlapping area; (4) the area of 

 distribution of a species may be broken by the area of another species 

 and then again be resumed (such an alternation of species may be re- 

 peated several times over) — a discontinuous area; (5) within the area 

 of distribution of a species there may be enclosed islet-like habitats of 

 another species, which, in addition, has its own main area, that may or 

 may not contain islet-like inclusions of the first species; (6) lastly, 

 there are cases when one of the species has an independent area, while 

 the other only has such islet-like habitats within the area of the first. 

 Ilyinsky (1933) proposed the following classification of areas, which 

 takes into account not only their statics but also their dynamics: 



1. Progressive or expanding areas 



1. Radiate area {area radiata) 



2. Fringed area (area fimbriata) 



3. Continuous area {area solidd) 

 II. Retrogressive or' conlracling areas 



4. Reticulate or perforated area {area perforata) 



5. Discontinuous or fragmented area {area disjunda or fragmentala) 



6. Area limited to one greatly restricted geographical region {area solitaria) 



The areas of species distributed both in the northern and southern 

 hemispheres but not in the tropical zone are called bipolar areas. 



Other types of areas, such as cosmopolitan, endemic, vicarious, 

 and relic areas, as well as continuous and discontinuous areas, we shall 

 discuss at greater length. 



Cosmopolitan and Endemic Areas: — There is only a very limited 

 number of species that are distributed over all or almost all the globe. 

 Species so distributed are, for the most part, those which are indiffer- 

 ent to environmental conditions, i.e., ubiquitous species. Such wide- 

 ranging species are known as cosmopolites or pan-endemics (Fenzl). 



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