296 THE ORIGIN OF SPECIES 



one section of the Malpigliiacese the closed flowers, 

 according to A. de Jussieu, are still further modified, 

 for the five stamens which stand opposite to the sepals 

 are all aborted, a sixth stamen standing opposite to a 

 petal being alone developed; and this stamen is not 

 present in the ordinary flowers of these species; the style 

 is aborted; and the ovaria are reduced from three to 

 two. Now although natural selection may well have had 

 the power to prevent some of the flowers from expand- 

 ing, and to reduce the amount of pollen, when rendered 

 by the closure of the flowers superfluous, yet hardly 

 any of the above special modifications can have been 

 thus determined, but must have followed from the laws 

 of growth, including the functional inactivity of parts, 

 during the progress of the reduction of the pollen and 

 the closure of the flowers. 



It is so necessary to appreciate the important effects 

 of the laws of growth that I will give some additional 

 cases of another kind; namely, of differences in the same 

 part or organ, due to differences in relative position on 

 the same plant. In the Spanish chestnut, and in certain 

 fir trees, the angles of divergence of the leaves differ, 

 according to Schacht, in the nearly horizontal and in the 

 upright branches. In the common rue and some other 

 plants, one flower, usually the central or terminal one, 

 opens first, and has five sepals and petals, and five divi- 

 sions to the ovarium; while all the other flowers on the 

 plant are tetramerous. In the British Adoxa the upper- 

 most flower generally has two calyx-lobes with the other 

 organs tetramerous, while the surrounding flowers gener- 

 ally have three calyx-lobes with the other organs pan- 

 tamerous. In many Compositse and Umbelliferse (and in 



