Means of Dispersal. 27 



and Cornwall, and of the peculiar eastern-county plants 

 belong to this group, the larger seeded species found 

 associated with them on the Continent being absent. 

 These plants seem therefore to possess in a pre-eminent 

 degree the power of crossing seas like that which separates 

 Ireland from the Pyrenees. They are probably trans- 

 ported freely by migrating birds, either on their feet or in 

 their feathers ; but the moist-soil species must also have 

 been carried in profusion in the cakes of mud which adhere 

 to the flanks of oxen that have rested in a moist meadow 

 till the earth has dried on them. Before fences were made, 

 the migrating horses, oxen, and bisons, in this way must 

 have carried such seeds for long distances, and any adhering 

 to the head of an animal would be carried across an arm 

 of the sea uninjured. It must be remembered, however, 

 that the autumn migration of mammals, which is the 

 migration when nearly all the seeds are ripe, would have 

 been southward in Britain, and consequently could only carry 

 plants in that direction. The northward migration taking 

 place in spring, few seeds would be carried, except such as 

 had become entangled in the fur and were shed with it 

 next summer. Wading and swimming birds, on the other 

 hand, commonly come to Britain from the north and east 

 in autumn, leaving the colder districts at a time when the 

 seeds are ripe, thus bringing the smaller ones to this 

 country. This is probably the reason why so large a pro- 

 portion of the minute-seeded Arctic plants are found in 

 Britain, though many of the species only occur in small 

 numbers and at various scattered localities. 



The next group, that containing the plants with large 

 edible unprotected seeds, is a small one in this country ; 

 but it is of especial importance on account of the difficulty 

 the species present when we try to account for their pre- 

 sence in these Islands, except on the hypothesis of a former 



