INDIRECT EQUILIBRATION. 447 



ing these longei' hairs, and the inheritance of successive incre- 

 ments of growth in the hairs, there may result a seed deviat- 

 ing greatly from the original. Other individuals of the 

 same species, subject to the different physical conditions of 

 other localities, may develop somewhat thicker or harder 

 coatings to their seeds : so rendering their seeds less digest' 

 ible by the birds that devour them. Such thicker-coated 

 seeds, by escaping undigested more frequently than thinner- 

 coated ones, T\'ill have additional chances of growing up and 

 leaving offspring ; and this process, acting in a cumulative 

 manner through successive years, will produce a seed diverg- 

 ing ia another direction from the ancestral type. Again, 

 elsewhere, some modification in the physiologic actions of 

 the plant, may lead to an unusual secretion of an essential 

 oil in the seeds ; which rendering them unpalatable to crea- 

 tures that would otherwise feed on them, may diminish the 

 destruction of the seeds, so giving an advantage to the variety 

 in its rate of multiplication ; and this incidental peculiarity 

 proving a preservative, will, as before, be gradually increased 

 by natural selection, until it constitutes another divergence. 

 Now in these and countless analogous cases, we see that plants 

 may become better adapted, or re-adapted, to the aggregate of 

 surrounding agencies, not through any direct action of sucli 

 agencies upon them, but through their indirect action — 

 through the destruction by them of the individuals which are 

 least congruous with them, and the survival of those which 

 are most congruous with them. All these slia;-ht variations 

 of function and structure, arising among the members of a 

 species, serve as so many experiments ; the great majority of 

 which fail, but a few of which succeed. Just as we see thai 

 each plant bears a multitude of seeds, out of which some two oi 

 three happen to fulfil all the conditions required for reaching 

 matuiTty, and continuing the race ; so we see that each species 

 is perpetually producing numerous slightly-modified forms, 

 deviating in all directions from the average, out of which 

 most fit the sivrrounding conditions no bettor than their pa- 



