E. V. Wulff —60— Historical Plant Geography 



It is of interest that among the species in this list are plants differ- 

 ing widely in habitat. There are fresh-water aquatics (15 floating or 

 submerged species and 23 species that root in the bottom of ponds or 

 lakes but extend the upper part of their stems and leaves above the 

 surface of the water) and, on the other hand, there are xerophytes 

 (14-15 species). Another 30 or so species are accounted for by weeds 

 infesting cultivated fields. The life span of these species also differs: 

 47 of them are annuals, 3 biennials, and 66 perennials. Likewise they 

 are distributed at random among the various groups of the vegetable 

 kingdom. 



For these wide-ranging species Molisch (1926) has proposed the 

 more accurate term "semi-cosmopolites". 



If we turn now to species not occupying such a large territory on 

 the earth's surface, we can note, as regards their distribution, two main 

 types. To the first belong species distributed in various regions and 

 countries; these are known as scattered, sporadic (de Candolle), or 

 polyendemic (Fenzl) species. In contrast to these, there are other 

 species which in their distribution are limited to a very restricted area, 

 not extending beyond some one region, country, island, or mountain 

 summit. Such species are called endemics. With respect to all these 

 terms, just as in the case of the term "cosmopolite", it must be re- 

 membered that they bear only a relative, often conditional, and by no 

 means absolute character. 



By endemic area, a concept first introduced into science by A. P. de 

 Candolle, we now understand the area of a taxonomic unit, particu- 

 larly of a species, limited in its distribution to some one natural region 

 or habitat, the physico-geographical and ecological conditions of which 

 set it off from adjoining regions. In this respect islands and mountain 

 peaks, with their distinct natural boundaries, make possible the most 

 exact determination of an endemic area. As regards other regions, 

 such a sharp delimitation rarely occurs. 



But the very concept "endemic" is not simple. There are different 

 interpretations and evaluations which depend largely on the age of the 

 endemic. In some cases the origin of an endemic should be referred to 

 remote times, judging by its phylogenetic antiquity, taxonomic isola- 

 tion, character of its habitats {e.g., mountain peaks or islands, which 

 have since time" immemorial been in a state of isolation), or its past 

 history. For example, to this group we may refer a species which at 

 one time had an extensive distribution but which later, during the 

 course of geological revolutions accompanied by climatic and physico- 

 geographical changes in habitat conditions, gradually died out and 

 eventually entirely disappeared from the greater part of its area, sur- 

 viving only in a small portion of the latter, thanks to some favorable 

 circumstances or other. Consequently, in ancient lands, as, for in- 

 stance, in mountain regions or on islands the vegetation of which has 

 survived during geological revolutions, the percentage of endemic 

 species is necessarily very high, and the endemism itself is of an 

 ancient, relic character. Hence, the number of relic endemics in the 

 composition of a given flora indicates both how old the latter is and 

 how long it has been isolated. The Alps, for instance, have 200 en- 

 demic species, the Canary Islands — 469 species (45% of the total), 



