OBJECTIONS TO THE THEORY OF NATURAL SELECTION 177 



a character which was considered by De Candolle to be in other 

 species of the highest systematic importance. Professor Braun 

 mentions a Fumariaceous genus, in which the flowers in the 

 lower part of the spike bear oval, ribbed, one-seeded nutlets; and 

 in the upper part of the spike, lanceolate, two-valved, and two- 

 seeded siliques. In these several cases, with the exception of that 

 of the well-developed ray-florets, which are of service in making 

 the flowers conspicuous to insects, natural selection cannot, as 

 far as we can judge, have come into play, or only in a quite sub- 

 ordinate manner. All these modifications follow from the relative 

 position and interaction of the parts; and it can hardly be doubted 

 that if all the flowers and leaves on the same plant had been sub- 

 jected to the same external and internal condition, as are the 

 flowers and leaves in certain positions, all would have been modi- 

 fied in the same manner. 



In numerous other cases we find modifications of structure, which 

 are considered by botanists to be generally of a highly important 

 nature, affecting only some of the flowers on the same plant, or 

 occurring on distinct plants, which grow close together under the 

 same conditions. As these variations seem of no special use to the 

 plants, they cannot have been influenced by natural selection. Of 

 their cause we are quite ignorant; we cannot even attribute them, 

 as in the last class of cases, to any proximate agency, such as 

 relative position. I will give only a few instances. It is so common 

 to observe on the same plant, flowers indifferently tetramerous, 

 pentamerous, etc., that I need not give examples; but as numerical 

 variations are comparatively rare when the parts are few, I may 

 mention that, according to De Candolle, the flowers of Papaver 

 bracteatum offer either two sepals with four petals (which is the 

 common type with poppies), or three sepals with six petals. The 

 manner in which the petals are folded in the bud is, in most 

 groups, a very constant morphological character; but Professor 

 Asa Gray states that with some species of Mimulus, the aestivation 

 is almost as frequently that of the Rhinanthideae as of the Antir- 

 rhinideae, to which latter tribe the genus belongs. Aug. Saint- 

 Hilaire gives the following cases: the genus Zanthoxylon belongs 

 to a division of the Rutaceae with a single ovary, but in some 

 species flowers may be found on the same plant, and even in the 

 same panicle, with either one or two ovaries. In Helianthemum the 

 capsule has been described as unilocular or trilocular; and in H. 

 mutabile, "Une lame plus ou moins large s'etend entre le pericarpe 

 et le placenta." In the flowers of Saponaria officinalis Dr. Masters 

 has observed instances of both marginal and free central placenta- 



