12 ON THE DISPERSAL OF SEEDS BY MAMMALS. 



I may here call attention to a fact which has been over- 

 looked by some naturalists in dealing- with this subject, name- 

 ly, that it is of no advantage to a plant to have .its seeds borne 

 to great distances but that on the contrary it may be posi- 

 tively injurious. In the first place the plants may be partially 

 or wholly unisexual, the male and female flowers being on 

 different trees. This is especially common among East Indian 

 jungle trees, notably in the orders Euphorbiaceae, Sapin- 

 dacese, and Myristicacese. 



Now if we suppose that a flock of pigeons have swooped 

 down upon a nutmeg tree in fruit and swallowed a quantity 

 of the seeds, and then flown away in all directions for, say, a 

 hundred miles before passing the seed, the plants will even- 

 tually be at so great a distance apart, that it will be impossible 

 for the flowers of the female trees to be fertilized, and such 

 isolated trees can never reproduce themselves. 



The same observation applies to plants which require a 

 special fertilizing insect. If the seed is borne to a district 

 where the fertilizer does not exist, it is to all intents and pur- 

 poses destroyed. In this case, however, it is possible that 

 another fertilizer may be found who can do the work fairly 

 well, and indeed it is rare that any plant depends on a single 

 species of fertilizer. And lastly there is always a risk of the 

 seeds being deposited in an unsuitable locality, if borne too 

 far away. This, however, is obviated by the conservative 

 habits of the agents, thus fruit pigeons which always inhabit 

 thick jungle, even if they did travel a long way with the seeds, 

 inasmuch as they naturally fly to thick jungle, would almost 

 certainly drop the seed in a locality similar to the one they took 

 it from, and in the same way wading birds carrying seeds 

 adhering to their feathers, would in their long migratory 

 flights pass over jungles and deserts and only stop at pools 

 or swamps where the seeds might get planted. 



In the matter of wind-dispersed seeds also it is not difficult 

 to show, especially in the flora of the big jungles, that travelling 

 for a long distance is of no object and indeed does not seem to 

 be aimed at. The object aimed at is rather to sprinkle the 

 seeds at such a distance from the parent tree that the roots of 



