CH. VI, 10] MORPHOLOGY OF FLOWERS 



323 



so that they likewise are leaves, of a linear or needle-like 

 sort. The anther, however, answers to nothing in a leaf, 

 and we hold it in reserve for a moment. In the pistil 

 each carpel has the leaf origin and anatomy, its development 

 being such that it infolds with the upper surface inward 

 (Fig. 221). Where the edges of the infolded leaves grow to- 

 gether, the tissues are enlarged, forming placentce (Fig. 222), 

 upon which stand the ovules, while the 

 tips of these leaves become prolonged and 

 modified to styles and stigmas. The ovules, 

 however, do not answer to anything in a 

 leaf, and we reserve them, like the anthers, 

 for the present. The receptacle is very 

 clearly a stem, enlarged at the tip to 

 bear the other floral parts. Sepals, petals, 

 stamens, and carpels all stand in whorls, 

 which, as with whorls of green leaves on 

 the stem, regularly alternate (page 140, and 

 Fig. 94), while other relations of phyllotaxy 

 occur in these parts. Furthermore, as with 

 ordinary leaves and stems, flowers originate 

 in buds, which are either terminal or axillary. 

 Thus the typical simple flower consists mor- 

 phologically of a branch, of limited, or 

 determinate, growth, containing whorls of 

 modified leaves borne close together at 

 the end of a stem, and surrounding two en- 

 tirely different kinds of structures, anthers 

 and ovules. 



We turn now to examine the morphological nature of 

 anthers and ovules, which involves the relations of flowers to 

 the reproductive structures of the lower kinds of plants. It 

 happens, unfortunately, that not all of the stages which 

 must have existed in the evolution of the flower are now 

 represented in existent plants ; but, as will be shown in 

 detail in Part II of this book, enough of the stages survive 



FIG. 221. Dia- 

 grammatic repre- 

 sentation of the 

 mode of union of 

 three carpellary 

 leaves into a one- 

 celled ovary. The 

 united edges form 

 the placentae, on 

 which the ovules 

 are borne. (After 

 Gray.) 



