INDIRECT EQUILIBRATION. 533 



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 digestible by the birds 

 which devour them. Such thicker-coated seeds, by escaping 

 undigested more frequently than thinner-coated ones, will 

 have additional chances of growing and leaving offspring; 

 and this process, acting in a cumulative manner season after 

 season, will produce a seed diverging in another direction 

 from the ancestral type. Again, elsewhere, some modification 

 in the physiologic actions of the plant may lead to an un- 

 usual secretion of an essential oil in the seeds; rendering 

 them unpalatable to creatures which would otherwise feed 

 on them : so giving an advantage to the variety in its rate 

 of multiplication. This incidental peculiarity, proving a 

 preservative, will, as before, be increased by natural selection 

 until it constitutes another divergence. Now in such cases, 

 we see that plants may become better adapted, or re-adapted, 

 to the aggregate of surrounding agencies, not through any 

 direct action of such agencies on them, but through their 

 indirect action through the destruction by them of the indi- 

 viduals least congruous with them, and the survival of those 

 most congruous with them. All these slight 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 each plant 

 bears a multitude of seeds, out of which some two or three 

 happen to fulfil all the conditions required for reaching 

 maturity and continuing the race; so each species is ever 

 producing numerous slightly-modified forms, deviating in all 

 directions from the average, out of which most fit the sur- 

 rounding conditions no better than their parents, or not so 

 well, but some few of which fit the conditions better; and, 

 doing so, are enabled the better to preserve themselves, and 

 to produce offspring similarly capable of preserving them- 

 selves. Among animals the like process results in 

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