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 Euphorbiaccæ, Sapin- dace, and Myristicace.
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 secd 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 trece that the roots of
