LONG FLIGHTS OF BIRDS 



acorn husks and a number of half-eaten, pecked acorns."^ 

 So that crows may have brought the acorns that colonized 

 Britain with oak forest in the earliest historical period. 



Another means of dispersal is not so obvious on the South 

 Downs. In the Arctic region a glacier breaks away at its 

 tongue into icebergs, which float off and are stranded some- 

 where perhaps hundreds of miles distant. Upon these ice- 

 bergs are stones and soil and plants which may be caiTied to 

 a great distance from their original place. In the Glacial 

 period or Great Ice Age, ice may have been an important 

 help in distributing plants, but at present it is difficult to 

 find a good example. 



From all this it is clear that in order to carry plants to 

 new countries and new homes, everything that moves on the 

 earth's surface can be employed. Not only the wind, but 

 ocean currents, river waters, icebergs, and floating ice are 

 used. Migrating birds, mammals, and especially the most 

 restless and unsettled animal of all, viz. man, are at work 

 consciously and deliberately, or unconsciously and accident- 

 ally, carrying the seeds to form new forest, grasslands, or 

 harvests in other countries. 



The subject is in truth so vast that it is difficult to select 

 the most interesting and important cases. 



The way in which squirrels, rats, voles, and lemmings 

 devour nuts and the like often leads to the distribution of 

 the fruit. A squirrel may, like a human being, forget where 

 its store was buried, or be driven from the place. Then 

 some of those forgotten nuts will grow into trees. 



Birds are known to travel enormous distances. It is said 



that one little Arctic bird travels from Heligoland to 



Morocco in a single flight. It would not, at first sight, 



* Reid, Origin of the British Flora. 

 R 257 



