THE FLOWER 



223 



appear to be thrown into rosettes or cycles. This change 

 does not necessarily affect all the parts simultaneously. 

 For example, in the common buttercup the sepals and 

 petals are nearly in cycles, while the carpels are spirally 

 arranged and indefinitely numerous on the head-like recep- 

 tacle (Fig. 202). On the other hand, in the common water- 



FlG. 203. 



Flower of water-lily (Nympficea), showing numerous petals and stamens. — 

 After Caspary. 



lily the petals and stamens are spiral, and indefinitely re- 

 peated, while the sepals and carpels are approximately 

 cyclic (Fig. 203). 



Finally, in the highest forms, all the floral organs are 

 in definite cycles, and there is no indefinite repetition of 

 any part. All through this evolution from the spiral to the 

 cyclic arrangement there is constantly appearing a tend- 

 ency to " settle down " to certain definite numbers. When 

 the complete cyclic arrangement is finally established these 

 numbers are established, and they are characteristic of 

 great groups. In cyclic Monocotyledons there are nearly 

 always just three organs in each cycle, forming what is 

 called a trimerous flower (Fig. 204) ; while in cyclic Dicot- 



