266 



THE CONTINUITY OF THE RACE 



parts — stamens, pistils, petals, and sepals, it is complete. Absence of any 

 of these parts makes the flower incomplete. These terms are sometimes 

 confusing, since we tend to think that if a thing is perfect it must also be 

 complete, but in the terminology of flowers this not so. A complete flower 

 is necessarily perfect, since it must have both stamens and pistils as well 

 as the other parts; but, as a little consideration will show, an incomplete 

 flower may be perfect, and an imperfect flower cannot be complete. 



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Fig. 17.12. Types of inflorescences. Flowers are indicated by small circles or ovals, leafy 

 bracts by short curved lines. A, spike; B, catkin or anient; C, spadix; D, head; E, raceme; 

 F, corymb; G, umbel; H, compound umbel; I, panicle; J, cyme; K, scorpioid cyme. (Re- 

 drawn from Hill, Overholts and Popp, Botany, 2d ed.) 



The number, arrangement, and form of the flower parts vary much 

 from group to group of the angiosperms and furnish the best characters 

 for their classification. The parts may be arranged in a spiral, or in the 

 much more frequent pattern of concentric circles called the cyclic arrange- 

 ment. All the petals and all the sepals may be alike, in which case the 

 flower is regular, like that of a lily or a wild plum ; or some of the petals 

 or sepals may be much larger or may be differently shaped than the 

 others, making the flower irregular, like that of the sweet pea. Often 

 the individual parts of one whorl or circle become fused together or fused 



