ruin 7 



CONDITIONS ON WHICH DISTRIBUTION DEPEND. 53 



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 phenomena 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 



