THE GENERAL SHAPES OF PLANTS. 129 



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. Formu- 

 las which express the shapes of entire plants in terms of sur- 

 rounding conditions, must be formulas which also express 

 the shapes of their several parts in terms of surrounding 

 conditions. If, therefore, we tiud 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 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 sur- 

 rounding 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. 



