io8o A TEXTBOOK OF THEORETICAL BOTANY 



is usually counterbalanced by the smaller size of the flowers, and the advan- 

 tage where insect visits are concerned seems to be rather in the relative 

 ease wdth which cross-pollination is efl^ected. 



The most condensed types frequently resemble single flowers, particu- 

 larly the capitula of various families, in which the resemblance is often 

 enhanced by the development of pseudo-petals around the capitulum, 

 through the alteration either of bracts or of the corollas of the peripheral 

 flowers (Fig. 1047). The most advanced types are almost certainly the 



Fig. 1047. — Centaiivea cyaniis. Capitulum showing disc 

 florets surrounded by highly modified ray florets. 



highly condensed forms in which there is specialization of function between 

 the individual flowers, as in the spadix (spike) of Arum or in the cyathium 

 (capitulum) of Euphorbia and in many Compositae. The degree of integra- 

 tion becomes, in certain cases, so great that the structure has both the 

 semblance and the biological character of a flower while the aspect of the 

 individual flowers is lost. The Euphorbiaceae show this in a remarkable 

 degree. Some genera have perfect flowers arranged in catkins. In others 

 the catkins have been condensed and show reduction. In Euphorbia the 

 catkin is so reduced that it (the cyathium) has the appearance of a simple 

 flower. In yet other types the cyathia themselves are reduced and grouped 

 into " incyathescences ", which a further reduction again brings down to 

 the aspect of a simple flower; two cycles of what has been called super- 

 evolution. There are indeed numerous instances which illustrate the value 

 and importance of the flower-model, by its re-emergence in condensed 



