Clare Island Survey — Phanerogamia. 10 67 



for long periods of time (see p. 93), might be present, even if plants could not 

 be found. Of the disappearance and reappearance of plants in certain stations 

 many strange instances are on record. 



While it may be freely admitted, then, that the frequent and violent 

 squalls and storms in mountain regions may transport even heavy seeds 

 far up and down the slopes, these occurrences are probably even there 

 exceptional, and have very little bearing on the question of dispersal across 

 undulating or level country. The presence of lofty buildings similarly 

 produces eddies and miniature whirlwinds, and aids seed-dispersal in towns. 

 Prof. Gwynne Vaughan has told me that in Chancery Lane, on a summer 

 day, with a light wind, a couple of years ago he has seen the air full of seeds 

 of Epilobium angustifolium, probably brought by eddies from the waste 

 ground at the Strand, where this plant appeared in quantity. 1 Had 

 buildings been absent, a much smaller number of these seeds would have 

 been lifted sufficiently to enable them to travel so far. Over flat country, 

 and especially over water, such upward eddies must be still fewer and less 

 powerful ; this point is discussed on a subsequent page (p. 72). 



In hot regions, the results of tornadoes, sand-storms, and kindred phenomena 

 prove that seed-transport over many miles is possible there ; but the lesson 

 drawn from these hardly applies to our latitudes. 



Plume Seeds. 



The most striking examples are to be found among the Compositae. 

 Indeed, in beauty and delicacy, the pappus of the Thistles and their allies 

 surpasses any other wind-dispersal mechanism found in the vegetable 

 kingdom. The question whether the pappus or other flying-mechanism 

 has been evolved by natural selection as an aid to dispersal does not concern 

 us here. It is by many writers considered so ; but it may be noted 

 that Bentham 2 says : — " That the pappus, indeed, is really and solely a 

 provision for the transport of the seed will scarcely be maintained, when we 

 consider, first, that in the great majority of more or less unisexual Com- 

 positae the pappus is much more developed on the male or sterile achenes 

 than on the female fertile ones, and that in a large number of Cynaroideae, 

 and even in many Cichoriaceae, the pappus separates so readily from the 

 achene that the clown we see floating in such quantities over a field of thistles 

 has, for the most part, left the achene enclosing the seed behind." And 

 Goebel remarks : — " Many arrangements which have hitherto been considered 



1 See Journal of Horticulture, lv, p. 122. 1907. ' Compositae, supra cit,, p. 573. 



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