CONDITIONS ON WHICH DISTRIBUTION DEPEND. $3 
Provision exists for the dispersion of seeds by the fall of 
the fruit, by the carrying power of the wind of rivers, and of 
the sea, by the adhesion of them to the hair of beasts and 
the feathers of birds, by the voiding of them uninjured by 
animals which have eaten the fruit in which they were 
produced, and by man, purposely, or without design, in 
his migrations and his journeyings. But of the seeds thus 
dispersed, millions, and it may be the vast majority, alight 
where there are awanting one or more of the conditions 
under which alone they can germinate, grow, flower, fruit, 
and bring that fruit to perfection; and if this be the case 
with one or other of these conditions, there the plant, herb, 
or tree will not be produced, and permanently retain posses- 
sion of the place: only where everything is favourable can 
a foothold for the plant be obtained and maintained. I say 
obtained and maintained for even where a plant may suc- 
ceed in obtaining a foothold, it may subsequently be dis- 
placed in the struggle for possession with other plants 
better adapted for growth in the existing condition of the 
locality at any time. The resulting geographical distribu- 
tion of plants, herbs, or trees, in any land at any time is 
the result of the influence of two conflicting operations,— 
dispersion and repression acting like the centrifugal and 
centripetal phenomona of gravitation, keeping the planet 
and satellite in their orbits, and the stone in the sling. 
But there is another aspect of the subject which is not 
without its interest to the student of botany, and in so far 
to the student of forest science, which is suggestive of 
differences in conditions in different localities or at 
different times. The vegetation of any region may be 
sparse, or it may be abundant; but also under either of 
these conditions the plants of any kind (genus) may be 
uniform or varied, nearly uniform, or greatly varied; 
presenting in the locality few or many different forms 
(species). There may be in any locality, as respects the 
former, abundant or sparse vegetation, but as respects 
the latter, a poor or a rich flora; profusion of individual 
