No. 4.] CKOSSING OF PLANTS. 35 



new characters or powers and new environments. Plants 

 which live during many generations in one place become 

 accustomed to the place, thoroughly fitted into its condi- 

 tions, 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 take advantage, 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 subject ; 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 permanent advantage over its former condition, and new 

 crossing or another change may be necessary ; yet there is 

 often 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 

 influence 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 in- 

 fluences 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 



