THEOR T OF NA TURAL SELECTION. v( )3 



fied, for the five stamens whicli stand opposite to the sepals 

 are all aborted, a sixth stamen standing opposite to a petal 

 being alone developed; and tiiis stamen is not present in 

 the ordinary flowers of this species; the style is aborted; 

 and the ovaria are reduced from three to two. Now al- 

 though natural selection may well have had the power to 

 prevent some of the flowers from expanding, and to reduce 

 the amount of pollen, wdien 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 func- 

 tional inactivity of parts, during the progress of the reduc- 

 tion 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 flrst, and 

 has five sepals and petals, and five divisions to the ovarium; 

 while all the other flowers on the plant are tetramerous. 

 In the British Adoxa the uppermost flower generally bas 

 two calyx-lobes with the other organs tetramerous, while 

 the surrounding flowers generally have three calyx-lobes 

 with the other organs pentamerous. In many CompositaB 

 and Umbellifera? (and in some other plants) the circum- 

 ferential flowers have their corollas much more developed 

 than those of the center; and this seems often connected 

 with the abortion of the reproductive organs. It is a more 

 curious fact, previously referred to, that the achenes 

 or seeds of the circumference and center sometimes differ 

 greatly in form, color and other characters. In Cartha- 

 mus and some other Compositae the central achenes alone 

 are furnished with a pappus; and in Hyoseris the same 

 head yields achenes of three different forms. In certain 

 irmbellifer,3e the exterior seeds, according to Tausch, are 

 orthospermous, and the central onecrelospermous, and this 

 is a character which was considered by De CandoUu to be iu 

 other species of the highest systematic importance. Pro- 



