tup: geographical distribution of plants. 109 



usually with indigestible coatings are carried long distances, ofttinies, 

 before they are left by their carriers. The widest distribution by 

 this agency is undoubtedly secured through the birds, for birds can 

 cover a much greater area within a limited time after a meal than 

 can animals, and moreover they can pass readily over those natural 

 barriers — hill ranges and smaller arms of the sea — which animals 

 cannot. But we must not over-estimate the importance of this 

 agency, for birds of the longest tlight are generally carnivorous, 

 and can only occasionally and accidentally get some seeds into 

 their crops when other birds are their prey. Still a wide dissemi- 

 nation of certain species is secured in this way, and some of our 

 edible berries are good examples. Those seeds which cling to the 

 hair or wool of animals also secure some scattering in this waj% 

 but it is limited, as mammals do not as a rule range as far as 

 birds. There is one peculiar case, however, in which a certain very 

 modest species is believed to be the most widely distributed in the 

 world (for modesty is no liar to success in the vegetable kingdom), 

 and this has been brought about by the agency of Inrds. That is 

 the case of our very common water-shield, Brasenia peltata ^ which 

 is scattered Avidely not only in North America, but is found also in 

 ponds in Asia, Africa, and Australia. As the species has not an 

 edible fruit, it is supposed that the ver}^ sticky fruits cling to the 

 feet of aquatic birds and are hence carried over greater distances 

 than would be possible in the case of edible fruits of the ordinary 

 kinds. In all of these cases of course the distribution is ultimately 

 limited by the purely ph3"sical conditions of which we have spoken, 

 and the competition from the forms already occupying the ground 

 to which the new seed is carried. 



The next great influence that we must consider is that of man. 

 Man is always prone to over-estimate his own importance, and 

 this applies with particular emphasis to his relation to the remainder 

 of Organic Nature. His influence upon the Plant Kingdom has 

 been far less than appears at first sight, and almost uniformly un- 

 favorable, and it is a fact that the remainder of the world would get 

 along better if he were to drop out of it altogether. We have to a 

 slight extent altered nature ; I doubt if we have improved it. 



The direct influence of man in carrying plants from place to 

 place will occur to you first. But this includes for the most part 

 forms cultivated for food or for ornament, and the majority of 

 them, if left to themselves in their new homes would soon be 



