J. W. REED ON PLANTS COLLECTED IN THE PYRENEES. 107 



Mr. Baker were Potamogeton lanceolatus and Eriocaulon septan- 

 gulare. Nor, in the consideration of any general question of plant 

 distribution, must we leave out the agencies of oceanic currents, 

 winds, and birds. Sir Joseph D. Hooker has told us that seeds 

 have germinated at Kew after floating in the sea for 3,000 miles, 

 and Darwin that dust is blown 1,000 miles over the ocean — the 

 dust of the Krakatoa explosion, as we all remember, was carried 

 much further — and the extreme minuteness of many seeds is well 

 known to everyone. Birds not only eat seeds directly, but also 

 prey on fresh- water fishes which eat them too, and, as Darwin has 

 also shown, carry seeds over the ocean " in their feet, beaks, and 

 stomachs." 



This being so, it is not a matter for surprise that in many parts 

 of the world what are clearly immigrant forms should be found 

 side by side with an indigenous flora. 



Whilst the interposition of seas, deserts, mountain ranges, and 

 even forest regions has done much to differentiate the floras of the 

 various portions of the earth's surface, climate has done more. 

 Generally speaking climate becomes more rigorous as we ascend, 

 and thus in climbing from the plain to the summits of mountains 

 like Mont Perdu, the Vignemale, or the Marbore (all about 11,000 

 feet high), we find well-marked zones of vegetation. From the 

 rich and fruitful one at the foot, we pass through fir forests, then 

 over green alps with their northern flora, until nothing but mosses 

 and lichens are seen — the latter at last appearing as splashes of 

 colour only, on the higher wind-swept rocks ; and finally on to the 

 eternal snows, their surface reddened here and there by the lowly 

 unicellular alga, Proto coccus nivalis. In some parts of the Pyrenees, 

 as in the Alps, it is possible to tell approximately the height to which 

 we have ascended by observing the plants ; but this is not always 

 so, for from various causes not yet fully determined, many upland 

 valleys and high passes of the same height have been found to vary 

 greatly in their mean temperature. 



There is also, without doubt, an intimate relation between the 

 chemical composition of soils and distribution, but in this, as in 

 other directions, there is much left to be worked out. It may 

 here be stated as a fact which generally holds good that plants do 

 not always grow where prima facie they might be expected to 

 flourish, such growth often being prevented by the presence of other 

 forms of vegetation in some respects better equipped for the struggle 



