118 PLANT-LIFE ON LAND [OH. 



for the vast expenditure of material upon them ? A first 

 result is the provision with a high degree of probability 

 for the maintenance of the race in full numbers. The 

 fisherman knows that if he takes a trout in a certain 

 pool its place will be almost certainly occupied before 

 long by another. Naturally such replacement of 

 individuals cannot occur with any degree of regularity 

 among the rooted plants of our area of sward. But 

 the enormous over-production tends in this direction, 

 and will suffice to secure a reasonable average over 

 all. A second advantage gained is the probability of 

 spread of the species to any new spot which is 

 favourable, and the incursions of alien plants fully 

 show how effective this may be, as soon as opportunity 

 offers. A third result, and certainly not the least 

 important, is that the overplus gives a basis for 

 Natural Selection, bringing as a consequence the 

 maintenance of the stamina of the race by the 

 elimination of weaklings, and the preservation of 

 favourable variations, with the consequent possibility 

 of advance to a state of higher efficiency. 



In late years there has been a definite tendency 

 to minimise the effect of Natural Selection. It is 

 hardly necessary to point out that Selection in itself 

 is not a factor of advance. Naturally it can only 

 contribute indirectly by the elimination of weaklings, 

 and by sifting out favourable variations from among 

 the vast number of potential lives. The ultimate 



