176 STUDY OF COMMON PLANTS. 



I. The petals, of whicli tlie two lateral ones resemble 



the sepals, but are narrower and more or less 



twisted, while the lower ^ is developed into a 



large sac, the lip or labellum. 



3. The essential organs. These have been greatly 



modified, and are united above into an organ 



called the column. Note 



a. The three stamens, the single sterile one forming 

 a broadly triangular body, the apex of which 

 projects slightly into the opening of the label- 

 lum, and the two lateral fertile ones, each 

 with a large anther on the under side. 



h. The fleshy stigma, arching under the sterile 

 stamen, the stigmatic surface covered with 

 minute papillse. This is seen to better advan- 

 tage after the removal of the floral envelopes. 



II. Having learned the parts of the flower, endeavor 

 next to understand their homologies. Such a study is 

 extremely interesting, showing as it does " how curiously 

 a flower may be moulded out of many separate organs, — 

 how perfect the cohesion of primordially distinct parts 

 may become, — how organs may be used for purposes 

 widely different from their proper uses, • — how other 

 organs may be entirely suppressed, or leave mere useless 

 emblems of their former existence, — and finally . . . 

 how enormous has been the amount of change which these 

 flowers have undergone from their parental or typical 

 form." 2 



1 "The lip (in the Orchidace») is really the upper petal, i.e. the one 

 next to the axis, but by a twist of the ovary of half a turn it is more com- 

 monly directed forward, and brought next to the bract." 



'Darwin, I.e., p. 234. 



