SPERMATOPHYTES 



133 



iect of the relation of insects to flowers is a very large one, 

 and will be presented in the following chapter. 



The great variation in the structure of the corolla is the 

 variation of chief service in classification, so far as the peri- 

 anth is concerned. A great many terms have been applied 

 to the different conditions of the corolla, and a few of the 

 most significant conditions are as follows. The simplest 

 kind of corolla is one in which the petals are free from one 

 another and are all alike. Such a corolla is said to be poly- 

 petalous (of " many petals ") and regular. In many flowers 



B 



E 



FIG. 103. Sympetalous flowers: A, bluebell; B, phlox; C, deadnettle; D, snap- 

 dragon ; E, toadflax ; C,' D, E are irregular flowers (bilabiate in this case) . After 

 GRAY. 



the petals appear as if united to form tubes, bells, funnels, 

 etc. (Figs. 102 and 103), and such a corolla is said to be 

 sympetalous (" petals together "). This sympetalous con- 

 dition is so constant in families of plants, that the highest 

 one of the three great groups of Angiosperms is named the 

 Sympetalce, because in all of its families the flowers are 

 sympetalous. In certain families the petals of a flower are 

 not all alike ; and then the corolla is said to be irregular. 

 For example, the sweet pea and its allies have very irregular 

 flowers, the petals being very much unlike, but the corolla 

 is polypetalous. In the snapdragon, which is sympetalous, 

 the rim of the tube has the appearance of two unequal lips, 

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