Chap. VII.] THEORY OF NATURAL SELECTION. 1 73 



rudimentary ; and in some species of Viola three stamens are in 

 this state, two retaining their proper function, hut 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 numher 

 of five to three. In one section of the Malpighiaceaj 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 expanding, 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 pro- 

 gress 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, clue 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 ; whilst 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, whilst the surrounding flowers generally have 

 three calyx-lobes with the other organs pentamerous. In many 

 Composite and Umbelliferaj (and in some other plants) the circum- 

 ferential flowers have their corollas much more developed 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 circumference and centre 

 sometimes differ greatly in form, colour, and other characters. In 

 Carthamus and some other Composita? the central achenes alone 

 are furnished with a pappus ; and in Hyoseris the same head yields 

 achenes of three different forms. In certain Umbellifera? the ex- 

 terior seeds, according to Tausch, are orthospermous, and the central 

 one ccelospermous, and this is a character which was considered by 

 De Candolle to be in other species of the highest systematic im- 



