4 The Rural Library. 



then, is inevitable, and it must be severe. It follows as a necessity that those 

 seeds grow or those plants live which are best fitted to grow and to live, or which 

 are fortunate enough to find a congenial foothold! It would appear at first 

 thought that much depends upon the accident of falling into a congenial place, 

 or one unoccupied by other plants or animals ; but inasmuch as scores of plants 

 are contending for every unoccupied place, it follows that everywhere only the 

 fittest can germinate or grow. In the great majority of cases, plants grow in a 

 certain place because they are better fitted to grow there, to hold their own, 

 than any other plants are ; and the instances are rare in which a plant is so 

 fortunate as to find an unoccupied place. We are apt to think that plants 

 chance to grow where we find them, but the chance is determined by law and 

 therefore is not chance ! 



Much of the capability of a plant to persist under all this struggle, 

 therefore, depends upon how much it varies ; for the more it varies the 

 more likely it is to find places of least struggle. It grows under various 

 conditions— in sun and shade, in sand and clay, by the seashore or upon 

 the hills, in the humidity of the forest or the aridity of the plain. In 

 some directions it very likely finds less struggle than in others, and in these 

 directions it expands itself, multiplies, and gradually dies out in other direc- 

 tions. So it happens that it tends to take on new forms or to undergo an 

 evolution. In the meantime, all the intermediate forms, which are at best 

 only indifferently adapted to their conditions, tend to disappear. In other 

 words, gaps appear which we call "missing links." The weak links break 

 and fall away, and what was once a chain becomes a series of rings. So the 

 "missing links" are among the best proofs of evolution. 



The question now arises as to the cause of these numerous vaii?t ■ 

 animals and plants. Why are no two individuals in nature exactly alike : : ne 

 question is exceedingly difficult to answer. It was once said that plants vf, . '' 

 because it is their nature to vary, that variation is a necessary function;;*; 

 much as growth or fructification. This really removes the 'question^?* 

 yond the reach of philosophy ; and direct observation leads us to think i 

 some variation, at least, is due to external circumstances. We af e now 1 '" 

 ing for the cause of variation along some of the lines of evolutico, an 

 are wondering if the varied surroundings, or, as Darwin put it, thij "cb^ 

 conditions of life, " may not actually induce variability. This coihhi 

 would seem to follow to some extent from the fact of the severe aid 

 versal struggle in nature whereby plants are constantly forced Into new.] 

 strange- conditions. But there is undoubtedly much variation whvh 

 sprung from, more remote causes, one of which it is my purpose to db< 

 here. 



In the lowest animals and plants the species multiplies by mean; 



