14 The Rural Library. 



and new environments. Plants which live during many generations in one 

 place become accustomed to the place, thoroughly fitted into its conditions, 

 and are in what Mr. Spencer calls a state of equilibrium. When either plant or 

 conditions change, new adjustments must take place, and the plant may find an 

 opportunity to expand in some direction in which it has before been held back ; 

 for plants always possess greater power than they are able to express. 

 "These rhythmical actions or functions [of the organism]," writes Spencer, 

 ' ' and the various compound rhythms resulting from their combinations, are 

 in such adjustment as to balance the actions to which the organism is sub- 

 ject. There is a constant or periodic genesis of forces, which, in their kinds, 

 amounts, and directions, suffice to antagonize the forces which the organism 

 has constantly or periodically to bear. If, then, there exists this state of 

 moving equilibrium among a. definite set of internal actions, exposed to a 

 definite set of external actions, what must result if any of the external 

 actions are changed ? Of course there is no longer an equilibrium. 

 Some force which the organism habitually generates is too great or 

 too small to balance some incident force, and there arises a residuary 

 force exerted by the environment on the organism or by the organism 

 on the environment. This residuary force — this unbalanced force — of 

 necessity expends itself in producing some change of state in the 

 organism." The good results, therefore, are processes of adaptation, 

 and when adaptation is perfectly complete the plant may have gained no per- 

 manent advantage over its former conditions, and new crossing or another 

 change may be necessary ; yet there is sometimes a permanent gain, as when 

 a plant becomes visibly modified by change to another climate. Now this 

 adaptive change may express itself in two ways, either by some direct in- 

 fluence upon the stature, vigor or other general character, or indirectly 

 upon the reproductive powers by which some new influence is carried to the 

 offspring. If the direct influences become hereditary, as observation seems 

 to show may sometimes occur, the two directions of modification may 

 amount, ultimately, to. the same thing. 



For the purposes- of this discussion it is enough to know that crossing 

 within the variety and change of stock within ordinary bounds are bene- 

 ficial, that the results in the two cases seem to flow from essentially the same 

 causes, and that crossing and change of stock combined give much better 

 results than either one alone. These processes are much more important 

 than any mere groping after new varieties, as I have already said, not only 

 because they are surer, but because they are universal and necessary means 

 of maintaining and improving both wild and cultivated plants. Even after 

 one succeeds in securing and fixing a new variety, he must employ these 

 means to a greater or less extent to maintain fertility and vigor. In the case 



