396 



GEOGEAPIIICAL DISTRIBUTION AND 



[Ch. XL, 



in a century, or a tliousand years^ it will be sufficient to 



om 



must 



whether they act slowly in relation to the jperiod of our obser- 



duration 



Let us trace the operation of this cause in connection with 

 others. A tempestuous wind bears the seeds of a plant 

 many miles through the air, and then delivers them to the 

 ocean ; the oceanic current drifts them to a distant continent • 

 by the fall of the tide they become the food of numerous 

 birds^ and one of these is seized by a hawk or eagle, which 

 soaring across hill and dale to a place of retreat^ leaves, after 

 devouring its prey, the unpalatable seeds to spring up and 

 flourish in a new soil. 



Mr. Darwin found that fresh-water fish eat the seeds of many 

 land and water plants, and as the same fish are often devoured 

 by birds, such seeds may be readily transported by them to 

 great distances. The same naturalist observed also that the 

 earth adhering to the feet of birds, often contains a variety 

 of seeds of plants ; and he mentions pne case where from a 

 ball of earth taken from the leg of a partridge he raised more 

 than 80 individual plants belonging to species both of 

 monocotyledons and dicotyledons.^ Insects are probably in- 

 strumental like birds in disseminating plants, for proofs have 

 lately been obtained (see Chapter XLI.) of the germinating 

 power of seeds swallowed by locusts and rejected in their dung. 



.bo 

 almost 



intimately 



might probably explain nearly all the instances of plants 

 inhabiting two points very remote from each other and not 

 found in places intermediate ; but some difficulties must 

 remain in accounting for the range of species so long as the 

 botanist confines his speculations to the present state of the 

 earth's physical geography and climate. Por the geologist 

 can show that great changes have taken place in the height 

 of the land and in the position of land and sea since the 



* Origin of Species, 4th edition, p. 432. 



