CHAP. VII.] THEORY OF NATURAL SELECTION. 161 



each other on the same plant. The ordinary and open flowers can 

 be intercrossed ; and the benefits which certainly are derived from 

 this process are thus secured. The closed and imperfect flowers 

 are, however, manifestly of high importance, as they yield with 

 the utmost safety a large stock of seed, with the expenditure of 

 wonderfully little pollen. The two kinds of flowers often differ 

 much, as just stated, in structure. The petals in the imperfect 

 flowers almost always consist of mere rudiments, and the pollen- 

 grains are reduced in diameter. In Ononis columnar five of the 

 alternate stamens are rudimentary; and in some species of Viola 

 three stamens are in this state, two retaining their proper function, 

 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 ordi- 

 nary 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 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 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 

 Compositae and Umbelliferse (and in some other plants) the cir- 

 cumferential 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 circum- 



