GENERAL PHINCIPLES. 



be done by calling in the aid of each and all these methods 

 to the very utmost extent possible. 



Lastly, to attempt any theoretical exposition of the evo- 

 lutionary history of flowers, considerable caution is required ; 

 for the causes of variation are generally so obscure, the 

 chances of seeing them in activity so small, and experimental 

 methods of verification well-nigh impossible, that specula- 

 tions on this subject cannot altogether escape the bounds of 

 hypothesis so as to become demonstrable facts. Hence 

 observations which I shall make later on, with reference to 

 the origin of existing floral structures, will not profess to be 

 anything more than theoretical, and at most only a " work- 

 ing hypothesis " for future investigations. 



The Structure of a Typical Flower. — Before consider- 

 ing how the innumerable forms 

 of flowers deviate from one 

 another, it is advisable to assume 

 some typical form or plan as a 

 preliminary basis to start from, 

 or to which all flowers, if pos- 

 sible, may be referred as a 

 standard. It would be quite 

 possible to adopt some kind of 

 flower as it exists in nature, 

 but as this would be arbitrary, 

 it may be better to take an ideal 

 type, and the diagram (Fig. 1) will answer the purpose, 

 in which the outermost circle is supposed to represent a 

 cross section of the five Sepals constituting the Calyx. The 

 second circle is that of the five Petals of the Corolla. Tlie 

 third stands for the Anthers of the five Stamens superposed 

 to the sepals ; the fourth being those of five Stamens super- 

 posed to the petals. These two whorls of stamens together 



Fig. 1.— Diagram of a typical flower. 



