MODIFICATIONS OF THE TLOKAL ORGANS. 183 



organs has been gradual, for in another species of the same 

 genus, the G-ratiola aurea, two minute filaments occupy the 

 place of two of the stamens, although no trace of the fifth is 

 observable. In Gerardia a pair .of perfect stamens a little 

 shorter than the other two, occupy the place of these filaments, 

 and the stamens are thus rendered didynamous. 



In the Labiatae or mint tribe, which are all pentamerous 

 flowers, the fifth stamen is suppressed altogether, and the didy- 

 namous form prevails ; or we have two long and two short 

 stamens, the filaments of each pair being unequally developed. 

 That didynamous stamens are the consequence of a defective 

 development of the organs, is evident from the fact that in 

 other genera of the same family the development of the organs 

 has been arrested at an earlier stage, so that the two short 

 stamens are either reduced to mere filaments, or are absent 

 altogether from the corolla, the flower being strictly speaking 

 diandrous. 



The symmetry and regularity of the floral organs is more 

 frequently disturbed by the defective development or entire 

 suppression of one or more of the organs of a verticil, than by 

 any other cause. Such deviations from the normal structure 

 are very common, in fact almost any' flower will discover them 

 to the intelligent student, and the principle when once clearly 

 understood may be extended almost indefinitely. 



We close our illustrations of this topic with the following 

 analysis of the Spring beauty (Claytonia), a very common but 

 remarkably unsymmetrical flower. (Fig. 82) is a diagram show- 

 ing the flower and its ground plan. It will be perceived that 

 the flower is complete, for the four verticils are present, some 

 of them being partially but not entirely suppressed ; that the 

 flower is regular, for all the pieces of each floral verticil are 



