GENERAL PRINCIPLES. 5 



different whorls, as well as of those of the indivddual members 

 of the whorls with regard to each other, 



" Cohesion " signifies the union of parts of any, but of the 

 same whorl. The original or ancestral condition of the 

 parts composing every whorl is presumed, on the principles 

 of evolution, to have been one of entire freedom ; so that 

 the members w^ere as completely separate or free as, for 

 example, they are in a Buttercup. Reversions to this con- 

 dition of freedom may occur, and then the process is called 

 " dialysis ; " as in the case of a polypetalous CamimnuJa 

 occasionally cultivated as a garden plant. 



" Adhesion " signifies the union of parts of different 

 whorls ; as well as that between the ovary and the recepta- 

 cular tube, constituting the so-called inferior ovary. I regard 

 adhesion as representing a more advanced or a more highly 

 differentiated state than that of cohesion. Reversions may 

 occur by " solution," which brings about a freedom of parts 

 normally united, as in the abnormal cases of Apples, double 

 Saxifrage, members of the U'mbeUifer<T, etc., which have all 

 their parts perfectly free, though with inferior ovaries under 

 ordinary circumstances. 



" Form " refers to the shape of the organs ; such as those 

 of sepals and petals upon which generic characters are so often 

 founded, the length of the filaments, and other peculiarities. 

 If all the parts of any whorl be exactly alike, it is said to 

 be " regular ; " if not, the w^horl wnll be " irregular." 



The above five principles constitute the most important 

 in accordance with which Nature has brought about the 

 infinite diversity which exists in the Floral world. There are 

 minor distinctions, hereafter to be considered, such as colours, 

 scents, etc. ; but they are of less importance in investigating 

 the causes at work which have evolved specific and generic 

 differences amongst flowering plants. 



