126 TRANSACTIONS, NATURAL HISTORY SOCIETF OK GLASGOW. 



plant was unknown before the railway operations 

 began. 



To enter fully into the changes which man has 

 effected directly and indirectly on the indigenous 

 floras of the various countries he inhabits would> 

 however, be a task demanding separate treatment. 



It only remains, in conclusion, to point out that 

 these various arrangements for the dispersion of 

 vegetable seeds owe their value not so much perhaps 

 to the circumstance that they enable plants to take 

 possession of new territory as to the fact that they 

 bring about a renewal of the soil or natural rotation 

 of crops, prevent close interbreeding, and, by the 

 variety to which they give rise, diminish the severity 

 of the struggle for existence on any given area. 

 In the animal kingdom these ends are secured by 

 the power of free and spontaneous movement 

 enjoyed by animals but denied to vegetables. Not- 

 withstanding this defect, these provisions for disper- 

 sion render possible that continual intercourse which 

 takes place among the vegetable inhabitants of the 

 earth. Passive and stationary as may seem the 

 aspect of the vegetation in any region, our observa- 

 tions only require to be extended over a sufficient 

 period to convince us that not only the individuals 

 but even the species are ever changing, old forms 

 migrating, new ones coming in to take their places, 

 old relations being broken up and fresh ones 

 established. Among the vegetable community, just 

 as among the human population, the members of 

 the same family in time become widely separated, 

 and the inhabitants of any limited area of the 

 earth's surface exhibit every variety of origin,, 

 name, and character. 



