CHAPTER III 



LAWS OF FLORAL STRUCTURE 



Meaning of the Term. — When we speak of a natural law as governing 

 a certain natural object, we refer merely to some observed mode or 

 manner of the existence of that object. Thus it is a law that water 

 flows downward, because that has been observed to be one of the 

 peculiarities of this substance. Similarly, warm air rises, wood burns 

 when fire is applied to it, and the sepals and petals of a flower possess 

 a similar form to that of the leaves of the plant on which they grow 

 and of which leaves they are homologues. Nevertheless, water will 

 sometimes run up hill because it is forced up, warm air sometimes does 

 not rise because it is confined, wood will not burn because it is wet or 

 otherwise fireproof, and the sepals and petals will not conform with the 

 leaves because some plants have no leaves, or because the influence of 

 some other law, known or unknown to us, has interfered with the action 

 of the one stated. 



Under the natural and unobstructed influence of the morphological 

 development of the flower from a branch and of its parts from the leaves 

 of that branch, the flower and its parts would possess certain definite 

 and typical characters. In the process of such development, howcA'er, 

 there is a constant tendency toward variation from the typical state, 

 the extent and direction of which variation are determined by the 

 external conditions and forces to which the living plant is subject, so 

 that, as a rule, flowers differ greatly from that typical state. A careful 

 study of all flowers will nevertheless show that their general plan of 

 structure is in accordance with these laws, with more or less variation 

 in the details. 



Modification of the Typical Flower. — We shall here consider the laws 

 of floral structure in relation to the following characters: The relative 

 number and position of parts of different kinds or of different series, as 

 those of the calyx compared with those of the corolla, or of the andro- 

 ecium compared with those of the gynaecium; the separation of each 

 part from every other, both of the same and of different kinds or series ; 

 a similarity in form and size of the parts composing any one series; 



