220 The Philippine Journal of Science 1917 
mainland a number of different methods have been effective in 
carrying seeds to the island. More species seem to have been 
introduced by birds than by any other single agency. Birds 
have also been effective in scattering seeds on the island as, 
with a single exception, all of the commonest tree species are 
distributed by them. Next to birds, wind has brought the largest 
number of species to the island. When the predominance of 
grasses is considered it would seem that this agency is respon- 
sible for the presence of the bulk of vegetation on the island. 
The relative effectiveness of the various methods of dispersal 
has been quite different in the case of Krakatau.'^^ Owing to 
the greater distance of Krakatau from the mainland the invasion 
by different species has been slower than on Volcano Island. 
Twenty-three years after the destruction of the vegetation of 
Krakatau this island was visited by Ernst who gives a list of 
the species that had been collected on it up to that time. This 
list includes ninety-two seed plants and sixteen Pteridophyta. 
Ocean currents had been the most important method by which 
phanerograms had reached the island. According to Ernst 39 
per cent had certainly been carried to the island by this means, 
while the number that might have been introduced by sea cur- 
rents amounted to 72 per cent of the total. The number of seed 
plants that almost certainly had been transported by wind 
amounted to 16 per cent, while the addition of those that might 
possibly have been carried by this method would bring the total 
to 32 per cent. Birds were apparently much less effective than 
the two agencies just mentioned. Ernst says that 10 per cent 
of the total were certainly introduced by this method while an 
additional 9 per cent may, possibly, have been so transmitted. 
A comparison of the invasion of Krakatau and Volcano Island 
shows a very apparent difference in the efficiency of dispersal 
by birds over long and short distances. Not only is the number 
of species distributed by this means much greater in the case 
of Volcano Island, but the percentage is also greater. This is 
in harmony with the observation of Kerner that the interval 
between eating and ejecting of food is in the case of most birds, 
from one and a half to three hours. Wind has carried many 
more species to Volcano Island than to Krakatau. This is, 
of course, due to the greater distance in the latter case. The per- 
centage of species introduced on Krakatau during the first four- 
^ Ernst, A., op. cit. 
“ Kerner, A., The Natural History of Plants. Translated by F. W. 
Oliver, 2: 864. 
