E. V. Wulff —124— Historical Plant Geography 



(endozoic dispersal); and (2) transport of seeds by adhesion to the 

 feathers, feet, or other parts of their bodies (epizoic dispersal). As 

 examples of the first type we may take the facts reported by Darwin 

 in his "Origin of Species". During two months he found in his garden 

 in the excrement of small birds the seeds of twelve different species, 

 some of which later germinated. Nevertheless, as Darwin points out, 

 he did not once observe a case of "nutritious seeds" passing through 

 the intestines of a bird uninjured. In this connection the duration of 

 time that a bird retains seeds in its crop is of significance. After a 

 bird has devoured a large number of seeds, they only gradually pass 

 into the gizzard, so that some of the seeds lie uninjured in the crop 

 for as much as 12-18 hours. During this time a bird might, if driven 

 by a gale, cover a distance of 500 miles. When birds of prey fall 

 upon such exhausted birds, "the contents of their torn crops might 

 thus readily get scattered" ("Origin of Species," 6th ed., 1911, p. 510). 

 Darwin also cites (I.e., pp. 511-512) a number of instances of the 

 finding of seeds in cakes of earth adhering to the feet and legs of birds. 

 He even cites such an extraordinary case as that of obtaining from one 

 lump of earth, weighing 6K oz., taken from the leg of a partridge sent 

 to him, seed that after a lapse of three years produced 82 plants, 

 12 monocotyledons and 70 dicotyledons, the latter belonging to at least 

 three different species. Despite our confidence in Darwin, it is very 

 hard to believe that such a large number of seeds could have adhered 

 to the leg of a bird by natural means. 



Hemsley (1885) was likewise incHned to ascribe much significance 

 to birds as a factor in the dispersal of plants. He denies the possibility 

 of the transport of seeds in this way over great distances, as Guppy 

 assumes to be possible (5,000-6,000 miles), but he considers it very 

 probable that birds may carry seeds, for example, from one island of 

 the Polynesian group to another. Birds and sea currents together play 

 an important role in the stocking of islands, particularly coral islands, 

 which otherwise would be deprived of vegetation and, consequently, 

 would be uninhabitable. The Bermuda Islands, in particular, owe their 

 vegetation, to a considerable degree, to these two factors. Hemsley 

 gives a list of 38 species of swamp plants, the seeds of which might be 

 borne by birds together with particles of mud adhering to their feet, 

 and 13 other species of plants with fleshy fruits that might be trans- 

 ported endozoically by birds. 



Nevertheless, it is impossible to regard these facts as universal, 

 and there are a considerable number of cases when the isolated habitats 

 of a species may be explained only by the former existence of a land- 

 bridge connecting these widely separated parts of an area. As an 

 example, Hemsley cites Phylica niiida of the family Rhamnaceae, 

 which has an extensive range, embracing a number of widely separated 

 islands, such as Tristan da Cunha, Reunion (Bourbon), Mauritius, 

 Amsterdam, and, perhaps, Madagascar. The character of the distri- 

 bution and the distance separating one station from another is such 

 as scarcely to give grounds for presuming the chance dispersal of this 

 plant by birds. 



Kerner (1898) conducted an extensive series of experiments on 

 feeding 16 species of birds with the seeds of 250 different species of 



