Clare Island Survey — Phanerogamia. 10 65 



distance dispersal, De Candolle, 1 from a careful review of the evidence, 

 expressed his disbelief in the efficacy of wind-carriage as a means of 

 dissemination across considerable obstacles. 



Bentham, writing eighteen years later of the plumed seeds of the Com- 

 positae, which are of all other groups best fitted for wide dispersal, says 2 : " The 

 most violent winds will not carry them above two or three miles : the 

 moment the pappus gets into a damper atmosphere it collapses, and when 

 once the seed has fallen to the ground it is very rarely again raised by the 

 wind." 



Kerner, 3 from a series of observations on the seeds deposited on the 

 moraines and glaciers of the Alps, comes to the conclusion that the crossing 

 from one to the other side of a valley is the most that the wind-borne 

 seeds achieve among the mountains. He suggests that light seeds are 

 caught in upward currents in hot weather, and remain high in the air during 

 the day, but in the evening fall close to the point of ascent. Humboldt 4 

 quotes a similar observation by Boussingault, grass and straws being carried 

 up some thousands of feet. Yogler and Pittier also place importance on 

 these vertical air-currents in the mountains. 5 But this phenomenon would 

 require a stronger and more continuous ascending current, due probably to 

 more intense insolation, than we ever get in these islands, coupled with an 

 absence of horizontal currents. 



Dewey, 6 in a good general account of the means of dispersal of plants, 

 writes : " The distance which this class of seeds may be carried by the wind 

 may easily be exaggerated, being ordinarily not more than two or three miles, 

 or in hurricanes perhaps ten or fifteen." 



Willis and Burkill,' in a very interesting paper on the plants found 

 growing on the tops of the pollard willows in the Cambridge district, find 

 that while about three-fourths of the eighty species observed were plants 

 specially adapted for dispersal by wind or birds, nevertheless the seeds were 

 rarely carried by their distributing mechanism to a distance of more than 



1 A. de Candolle : Geogiaphie Botanique Raisonnee, ii, pp. 613-14. 1855. 



2 6. Bentham : On the Compositae (supra cit.), p. 573. 



3 A. Keener: Der Einfluss der Winde auf die Verbreitung dev Samen im Hochgebirge. 

 Zeitschrift des Deutschen Alpenvereins, ii, pp. 144-172. Epitomized in Gardeners' Chronicle, 

 1872, pp. 143-144 ; and in Nature, vi, pp. 164-165. 1872. 



4 A. von Humboldt : Tableaux de la Nature (English ed.), ii, pp. 33, 34. 1849. 

 6 P. Vogler, loo. cit. 



6 L. H.Dewey: Migration of Weeds. Yearbook of the Dept. of Agriculture, U.S.A., 1896, 

 p. 267. 



'J. C. Willis and I. H. Burkill: Observations on the Flora of the Pollard Willows near 

 Cambridge. Proc. Cambridge Phil. Soc, viii, pp. 82-91. 1895. 



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