372 DARWINISM 



CHAP. 



or perish, and all wliicli come within sight of an island will 

 struggle to reach it as their only refuge. But, with mountain 

 summits the case is altogether different, because, being sur- 

 rounded by land instead of by sea, no bird would need to fly, 

 or to be carried by the wind, for several hundred miles at a 

 stretch to another mountain summit, but would find a refuge 

 in the surrounding uplands, ridges, valleys, or plains. As a 

 rule the birds that frequent lofty mountain tops are peculiar 

 species, allied to those of the surrounding district ; and there 

 is no indication whatever of the passage of birds from one 

 remote mountain to another in any way comparable with 

 the flights of birds which are known to reach the Azores 

 annually, or even with the few regular migrants from 

 Australia to New Zealand. It is almost impossible to con- 

 ceive that the seeds of the Himalayan primula should have 

 been thus carried to Java ; but, by means of gales of wind, . 

 and intermediate stations from fifty to a few hundred miles 

 apart, where the seeds might vegetate for a year or two and 

 produce fresh seed to be again carried on in the same 

 manner, the transmission might, after many failures, be at 

 last effected. 



A very important consideration is the vastly larger scale 

 on which wind-carriage of seeds must act, as compared with 

 bird-carriage. It can only be a few birds which carry seeds 

 attached to their feathers or feet. A very small proportion of 

 these would carry the seeds of Aljjine plants ; while an almost 

 infinitesimal fraction of these latter would convey the few 

 seeds attached to them safely to an oceanic island or remote 

 mountain. But winds, in the form of whirlwinds or tornadoes, 

 gales or hurricanes, are perpetually at work over large areas 

 of land and sea. Insects and light particles of matter are 

 often carried up to the tops of high mountains ; and, from the 

 very nature and origin of "vvinds, they usually consist of 

 ascending or descending currents, the former capable of 

 suspending such small and light objects as are many seeds 

 long enough for them to be carried enormous distances. For 

 each single seed carried away by external attachment to the 

 feet or feathers of a bird, countless millions are probably 

 carried away by violent winds ; and the chance of conveyance 

 to a great distance and in a definite direction must be many 



