176 THE ORIGIN OF SPECIES 



alternate stamens are rudimentary; and in some species of Viola 

 three stamens are in this state, two retaining their proper func- 

 tion, but being of very small size. In six out of thirty of the closed 

 flowers in an Indian violet (name unknown, for the plants have 

 never produced with me perfect flowers), the sepals are reduced 

 from the normal number of five to three. In one section of the 

 Malpighiaceae 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 this species; the style is aborted; and the 

 ovaria are reduced from three to two. Now although natural selec- 

 tion may well have had the power to prevent some of the flowers 

 from expanding, and to reduce the amount of pollen, when ren- 

 dered 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 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 first, 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 has two calyx-lobes with 

 the other organs tetramerous, while the surrounding flowers gen- 

 erally have three calyx-lobes with the other organs pentamerous. 

 In many composite and umbelliferse (and in some other plants) 

 the circumferential flowers have their corollas much more devel- 

 oped than those of the centre; 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 cir- 

 cumference and centre sometimes differ greatly in form, color, 

 and other characters. In Carthamus and some other compositse 

 the central achenes alone are furnished with a pappus; and in 

 Hyoseris the same head yields achenes of three different forms. 

 In certain umbelliferae the exterior seeds, according to Tausch, 

 are orthospermous, and the central one coelospermous, and this is 



