E. V. Wulff —12— Historical Plant Geography 



include sea and river currents, atmospheric currents, animals, and man. 

 If these four means of seed dispersal are kept in mind, "one will iind, 

 I believe, that they are fully adequate to explain the finding of a small 

 number of plants common to different continents . . . Their combined 

 action — slow, steady, imperceptible — constantly tends to disperse plants 

 in all directions, and these plants become naturalized where they find 

 conditions favorable for their existence" (p. 410). 



After the appearance of the above-mentioned works it was possible 

 to publish the principles of the new science, the first attempt in this 

 direction being ScHOUw's "Grundziige einer allgemeinen Pflanzengeo- 

 graphie", issued in Danish in 1822 and translated into German in 1823. 

 To the development of historical plant geography, however, this work 

 contributed nothing, since its author makes a sharp distinction between 

 "plant geography" proper and the "history of plants", to which latter 

 he refers all problems with which historical plant geography is con- 

 cerned. Thus, WiLLDENOw's term "history of plants", embracing all 

 botanical geography, is narrowed down by ScHOUw, who includes in it 

 only problems of the history and genesis of species and floras, which 

 even earlier, as we have seen, were touched upon by Stromeyer. 

 ScHOXJW regards the "history of plants" as an independent science. 

 "The history of plants . . . does not constitute a part of physical 

 geography, since it is not a descriptive science, but rather a part of the 

 history of the earth, inasmuch as the latter treats not only of inorganic 

 but also of organic bodies" (p. 10). 



In another similar work by Meyen, "Grundriss der Pflanzen- 

 geographie", which appeared thirteen years after ScHOtJw's book, we 

 also find almost nothing concerning historical plant geography, with 

 the exception of a few pages devoted to problems of areas of distribu- 

 tion and their determination. 



In contrast to these works, a considerable contribution to historical 

 plant geography was made by Unger's "Versuch einer Geschichte der 

 Pflanzenwelt", which appeared in 1852. This book, speaking in 

 present-day terminology, may be considered a treatise on paleobotany, 

 embracing, however, relations between fossil and existing floras. The 

 introduction to this book, in which the author discusses the distribution 

 of plants, constitutes a notable contribution to historical plant geog- 

 raphy. 



Although the development of this new branch of knowledge, as we 

 have seen, had its expression in a number of works inspired in con- 

 siderable measure by von Humboldt, the credit for elaborating the 

 latter's ideas and for making the first synthesis of the new science of 

 historical plant geography belongs to Alphonse de Candolle. In his 

 chief work, pubHshed in 1855 and entitled "Geographie botanique 

 raisonnee ou exposition des faits principaux et des lois concernant la 

 distribution geographique des plantes de I'epoque actuelle", de Can- 

 dolle, as is clear from the title itself, undertook the task of elucidating 

 the laws of the distribution of plants. His understanding of what this 

 task involves is set forth in the preface to this work (pp. xi-xii) : — 



"Plants have a habitat conforming to the climate only under certain circumstances, 

 only in certain countries; there is not a single botanist but who knows that a species can 

 ordinarily live and reproduce itself far from its native home and that no country contains 



