Chapter II — 11 — 



History 



cata", which treats of the distribution of plants as Hnked with the 

 history of the settlements and migrations of men and animals. 



Nevertheless, it is Alexander von Hxjmboldt who should be re- 

 garded as the founder of plant geography, including also problems of 

 the origin of floras, since it was he who, in his "Essai sur la Geogra- 

 phic des Plantes" ("Ideen zu einer Geographic der Pflanzen" in the 

 German edition), appearing in 1807, established this new science and 

 gave it its present name. In this work Humboldt sets forth his ideas, 

 which embrace the bases of modern botanical geography, including 

 problems with which historical plant geography is concerned: 



"In order to come to a decision as to the existence in ancient times of a connection 

 between neighboring continents, geology bases itself on the analogous structure of coast- 

 lines, on the similarity of animals inhabiting them, and on ocean soundings. Plant geo''- 

 raphy furnishes most important material for this kind of research. It can, up to a certafn 

 pomt, determine the islands which, at one time united, have become separated from one 

 another; it finds that the separation of Africa and South America occurred before the 

 development of living organisms. It is again this science that shows which plants are com- 

 mon to both eastern Asia and the coastlands of Mexico and California, and whether there 

 are some which grow in all zones and at all altitudes. It is by the aid of plant geography 

 that we can go back with some certainty to the initial physical state of the globe It is 

 this science which can decide whether, after the recession of the waters to whose abundance 

 and movements the calcareous rocks attest, the entire surface of the earth was covered 

 simultaneously with diverse plants, or whether, according to the ancient myths of various 

 peoples, the globe, having regained its repose, first produced plants only in a single region 

 from which the sea currents carried them progressively, during the course of centuries into 

 the most distant zones" (pp. ig-20)*. ' 



No less definitely is put the question as to the importance of a 

 study of the past and present distribution of organisms: "In order to 

 solve the great problem as to the migration of plants, plant geography 

 descends into the bowels of the earth; there it consults the ancient 

 monuments which nature has left in the form of petrifactions in the 

 fossil wood and coal beds which constitute the burial-places of the first 

 vegetarion of our planet" (p. 22). The finding in temperate zones of 

 the remains of plants and animals of warmer climes puts to the fore 

 the question as to the former climatic conditions in the given localities. 



A still more detailed understanding of the tasks of botanical geog- 

 raphy we find in the works of Augustin P. de Candolle, who in his 

 "Essai Elementaire de Geographic Botanique" (1820), and also in 

 other works, clearly distinguishes between the "habitation" and the 

 "station" of a plant, meaning by the first the distribution of a plant 

 over the earth's surface and by the second its habitat conditions as a 

 whole. Thus, the section of this work entitled "Des habitations" 

 constitutes in considerable measure historical plant geography as he 

 understood it. In this chapter he does not limit himself to establishing 

 the habitats of plants but attempts to determine the causes underlying 

 this or that kind of distribution. Factors such as seas, deserts, moun- 

 tain chains, swamps, forests, and variarions in altitude constitute 

 obstacles to dispersal. Plants are endowed in different degree with the 

 ability to overcome these obstacles, and are dependent in great meas- 

 ure on passive factors as an aid in surmounting them. Such factors 



* Cited from the French edition. 



