Chapter VIII —117— Natural Factors 



data of this study is that in the Alps the higher the altitude, the lower 

 the percentage of species possessing adaptations for the dissemination of 

 their seeds or fruits by animals and the higher the percentage of wind- 

 dispersed species. 



These data fully suffice to assure us that seeds and fruits are dis- 

 persed by the wind and that by strong winds they may be borne for a 

 considerable distance from the place of their formation. This conclu- 

 sion is beyond dispute. Other questions, however, arise: To what 

 extent are such seeds capable of germinating and taking root under 

 the new conditions? Over what distances may seeds be borne by 

 wind? What significance does wind have as a factor in the "saltatory" 

 dispersal of plants (dispersal to widely separated locahties), i.e., as a 

 factor in the discontinuous distribution of plants? Unfortunately, we 

 have very few concrete data as to the transport of seeds and fruits by 

 wind, and indirect proofs or data that are not exact are always subject 

 to dispute. This accounts for the wide divergence of opinion with 

 respect to the evaluation of the significance of wind in the transport of 

 seeds over great distances. 



Among investigators ascribing great significance to wind in the 

 dispersal of seeds and considering that discontinuous areas may arise 

 as a result of the transport of seeds by wind is Vogler, who in the 

 work already cited lists twelve concrete facts of such dispersal. Ac- 

 cording to data presented by him, seeds have been borne by the wind 

 over mountain peaks more than 2,000 m. in height; horizontally, the 

 maximum distances noted by him for the wind-transport of seeds are: 

 25 km. for Cardamine resedifolia, 9 km. for Galeopsis speciosa, 3 km. for 

 Serratula rhaponticum and Arabis turrita. Despite the great signifi- 

 cance ascribed by Vogler to wind in the dispersal of plants, we find 

 even in his own conclusions small grounds for his belief in the important 

 role of wind in the origin of discontinuous areas. Thus, he concludes 

 (p. 75) that the transport of seeds by wind for great distances, even for 

 hundreds of kilometers, is possible, but practically such long-distance 

 wind-transport plays a very limited role in the dispersal of plants; of 

 great significance is the wind-transport of seeds up to 40 km. and also 

 such transport over high mountain ranges. 



Vogler's work, therefore, as he himself points out, proved irref- 

 utably the significance of wind as a factor in the gradual dispersal of 

 plants, particularly as regards the invasion of territory with land as yet 

 unoccupied by vegetation, such as inaccessible cliffs and canyons. 

 However, as a proof of the "saltatory" dispersal of plants, as an aid to 

 an understanding of discontinuous areas, it contributed nothing, since 

 the isolated habitats mentioned by him either are located at relatively 

 short distances from one another, or are clearly of a chance nature, or 

 may be fully explained by the local topography of the area. 



Let us now examine the arguments of those investigators who con- 

 sider that the wind plays an insignificant role in the dissemination of 

 seeds over great distances. Alphonse de Candolle, in his "Geogra- 

 phic Botanique", pointed out that wind is often a factor in the dis- 

 persal of plants to the extent of transporting their seeds within the 

 Umits of their habitats or to adjacent territories. In many cases the 

 seeds ahght in places where their growth and further development is 



