144 MORPHOLOGICAL DEVELOPMENT. 



If organic form is determined by the distribution of forces, 

 and the approach in every case towards an equilibrium of 

 inner actions with outer actions; then this relation between 

 forms and forces must hold alike in the organism as a whole 

 in its proximate units, and in its units of lower orders. For- 

 mulas which express the shapes of entire plants in terms of 

 surrounding conditions, must be formulas which also express 

 the shapes of their several parts in terms of surrounding 

 conditions. If, therefore, we find that a plant as a whole is 

 radially symmetrical or bilaterally symmetrical or asymme- 

 trical, according as the incident forces affect it equally on all 

 sides of an axis, or affect it equally only on the opposite sides 

 of one plane, or affect it equally in no two directions; then, 

 we may expect that, in like manner, each member of a plant 

 will display radial symmetry where environing influences are 

 alike along many radii, bilateral symmetry where there is 

 bilateralness of environing influences, and unsymmetry or 

 asymmetry where there is partial or entire departure from a 

 balance of surrounding actions. 



To show that this expectation is borne out by the facts, 

 will be the object of the following four chapters. Let us 

 begin with the largest parts into which plants are divisible; 

 and proceed to the successively smaller parts. 



