xu GEOGRAPHICAL DISTRIBUTION OF ORGANISMS 361 



powerful means of dispersal the distribution of insects over 

 the entire globe, and their presence in the most remote 

 oceanic islands, offer no difficulties. 



The Dispersal of Plants. 



The dispersal of seeds is effected in a greater variety of 

 ways than are available in the case of any animals. Some 

 fruits or seed-vessels, and some seeds, will float for many 

 weeks, and after immersion in salt water for that period 

 the seeds will often germinate. Extreme cases are the double 

 cocoa-nut of the Seychelles, which has been found on the coast 

 of Sumatra, about 3000 miles distant; the fruits of the 

 Sapindus saponaria (soap-berry), which has been brought to 

 Bermuda by the Gulf Stream from the West Indies, and has 

 grown after a journey in the sea of about 1500 miles ; and the 

 West Indian bean, Entada scandens, Avhich reached the Azores 

 from the West Indies, a distance of full 3000 miles, and after- 

 wards germinated at Kew. By these means we can account 

 for the similarity in the shore flora of the Malay Archipelago 

 and most of the islands of the Pacific ; and from an examination 

 of the fruits and seeds, collected among drift during the voyage 

 of the Challenger, Mr. Hemsley has compiled a list of 121 

 species which are probably widely dispersed by this means. 



A still larger number of species owe their dispersal to birds 

 in several distinct ways. An immense number of fruits in all 

 parts of the world are devoured by birds, and have been 

 attractively coloured (as we have seen), in order to be so 

 devoured, because the seeds pass through the birds' bodies and 

 germinate where they fall. We have seen how frequently 

 birds are forced by gales of wind across a wide expanse of 

 ocean, and thus seeds must be occasionally carried. It is a 

 very suggestive fact, that all the trees and shrubs in the Azores 

 bear berries or small fruits which are eaten by birds ; while all 

 those which bear larger fruits, or are eaten chiefly by mammals 

 — such as oaks, beeches, hazels, crabs, etc. — are entirely 

 wanting. Game-birds and waders often have portions of mud 

 attached to their feet, and Mr. Darwin has proved by experi- 

 ment that such mud frequently contains seeds. One partridge 

 had such a quantity of mud attached to its foot as to contain 

 seeds from which eighty -two plants germinated; this proves that 



