Chapter VIII —119— Natural Factors 



wind, it is necessary to distinguish between the transport of the downy 

 plumes alone and the transport of plumes still bearing the seeds or 

 achenes. Records of distant flights refer chiefly to the plumes alone; 

 as to how far they flew with the fertile achenes still attached data are 

 entirely lacking. 



Ilyinsky (1933) thus records his observations on the wind-dispersal 

 of spruce seeds {Picea excelsa) in the upper Volga Basin: "Seeds once 

 fallen to the ground did not move any farther at all or made but very 

 short hops, the entire distance between them and the mother tree being 

 measured at the most in tens of meters." According to Schmidt 

 (1918), the distance to which seeds and fruits provided with special 

 adaptations for flight may be carried by the wind is not more than a 

 few kilometers and, in some cases, not over a few meters, e.g., the 

 birch — 1.6 km., the maple — 0.09 km., and the ash — 0.02 km. 



Bentham (1873) points out that the role of wind-borne seeds in the 

 dispersal of species of Compositae, according to data assembled by him, 

 is less than in the Leguminosae, Labiatae, and other families not 

 possessing any adaptations for seed dissemination. His investigations 

 showed that only 60 species of this family, i.e., not over 0.67 per cent 

 of the entire number of its species, are characterized by "saltatory" 

 dispersal by whatever agency, including accidental transport by man, 

 while the other 99.33 per cent of the species either remained within the 

 limits of their initial areas or spread farther by a gradual extension of 

 their area. 



Discussing the wind as a factor in the geographical dispersal of 

 seeds, particularly of the Compositae, Bentham confirms the conclusion 

 of DE Candolle and Kerner as to the inability of plumes to bear 

 fruits over great distances, especially over the sea. A very strong wind 

 cannot carry them farther than two or three miles, due to the fact that, 

 once the plumes encounter humid atmosphere, they become stuck to- 

 gether, causing the fruits to fall to the ground, whence they are only 

 very rarely borne farther by the wind. Thus, plumes can transport 

 seeds only short distances from the mother plants, and the only way in 

 which they might facilitate the migration of species is by accidentally 

 aiding the seeds being blown into streams, bales of goods, or soil 

 carried as ballast, whence they might be carried much farther. That 

 the role of plumes in plant migration is of slight significance is indi- 

 cated also by the fact that of the 60 species mentioned above as char- 

 acterized by "saltatory" dispersal only 22 or 23, or about one-third, 

 have plumes, whereas over two-thirds of the species of Compositae are 

 provided with them. 



Ridley (1930; pp. 71 and 130), despite his strong tendency to 

 ascribe to natural factors and particularly the wind very great 

 significance in the dispersal of plants, writes that winged fruits and 

 seeds are carried by the wind for only a relatively short distance, "not 

 more than i mile or so". 



On the basis of the foregoing data we feel fully justified in con- 

 cluding that the wind is a very important factor in the dissemination 

 of seeds over short distances but has little significance in their trans- 

 port over long distances, and that, consequently, most discontinuous 

 areas cannot be explained by its action. 



