[Footnote 136: Burchell's _Travels_, vol. i. p. 10.]
[Footnote 137: _Nature_, vol. iii. p. 507.]
[Footnote 138: _Flowers, Fruits, and Leaves_, p. 128 (Fig. 79).]
[Footnote 139: For a popular sketch of these, see Sir J. Lubbock's _Flowers, Fruits, and Leaves_, or any general botanical work.]
[Footnote 140: _Nature_, vol. xv. p, 117.]
[Footnote 141: Grant Allen's _Colour Sense_, p. 113.]
[Footnote 142: Canon Tristram's _Natural History of the Bible_, pp. 483, 484.]
[Footnote 143: For a complete historical account of this subject with full references to all the works upon it, see the Introduction to Hermann Müller's _Fertilisation of Flowers_, translated by D'Arcy W. Thompson.]
[Footnote 144: For the full detail of his experiments, see _Cross-and Self-Fertilisation of Plants_, 1876.]
[Footnote 145: See Darwin's _Fertilisation of Orchids_ for the many extraordinary and complex arrangements in these plants.]
[Footnote 146: The English reader may consult Sir John Lubbock's _British Wild Flowers in Relation to Insects_, and H. Müller's great and original work, _The Fertilisation of Flowers_.]
[Footnote 147: Müller's _Fertilisation of Flowers_, p. 248.]
[Footnote 148: "Alpenblumen," by D.H. Müller. See _Nature_, vol. xxiii. p. 333.]
[Footnote 149: This peculiarity of local distribution of colour in flowers may be compared, as regards its purpose, with the recognition colours of animals. Just as these latter colours enable the sexes to recognise each other, and thus avoid sterile unions of distinct species, so the distinctive form and colour of each species of flower, as compared with those that usually grow around it, enables the fertilising insects to avoid carrying the pollen of one flower to the stigma of a distinct species.]
[Footnote 150: See H. Müller's _Fertilisation of Flowers_, p. 18.]
[Footnote 151: The above examples are taken from Rev. G. Henslow's paper on "Self-Fertilisation of Plants," in _Trans. Linn. Soc._ Second series, _Botany_, vol. i. pp. 317-398, with plate. Mr. H.O. Forbes has shown that the same thing occurs among tropical orchids, in his paper "On the Contrivances for insuring Self-Fertilisation in some Tropical Orchids," _Journ. Linn. Soc._, xxi. p. 538.]
[Footnote 152: These are the numbers given by Darwin, but I am informed by Mr. Hemsley that many additions have been since made to the list, and that cleistogamic flowers probably occur in nearly all the natural orders.]
[Footnote 153: For a full account of cleistogamic flowers, see Darwin's _Forms of Flowers_, chap. viii.]
[Footnote 154: Henslow's "Self-Fertilisation," _Trans. Linn. Soc._ Second series, _Botany_, vol. i. p. 391.]
[Footnote 155: The Rev. George Henslow, in his _Origin of Floral Structures_, says: "There is little doubt but that all wind-fertilised angiosperms are degradations from insect-fertilised flowers.... _Poterium sanguisorba_ is anemophilous; and _Sanguisorba officinalis_ presumably was so formerly, but has reacquired an entomophilous habit; the whole tribe Poterieae being, in fact, a degraded group which has descended from Potentilleae. Plantains retain their corolla but in a degraded form. Junceae are degraded Lilies; while Cyperaceae and Gramineae among monocotyledons may be ranked with Amentiferae among dicotyledons, as representing orders which have retrograded very far from the entomophilous forms from which they were possibly and probably descended" (p. 266).
"The genus Plantago, like _Thalictrum minus_, Poterium, and others, well illustrate the change from an entomophilous to the anemophilous state. _P. lanceolata_ has polymorphic flowers, and is visited by pollen-seeking insects, so that it can be fertilised either by insects or the wind. _P. media_ illustrates transitions in point of structure, as the filaments are pink, the anthers motionless, and the pollen grains aggregated, and it is regularly visited by _Bombus terrestris_. On the other hand, the slender filaments, versatile anthers, powdery pollen, and elongated protogynous style are features of other species indicating anemophily; while the presence of a degraded corolla shows its ancestors to have been entomophilous. _P. media_, therefore, illustrates, not a primitive entomophilous condition, but a return to it; just as is the case with _Sanguisorba officinalis_ and _Salix Caprea_; but these show no capacity of restoring the corolla, the attractive features having to be borne by the calyx, which is purplish in Sanguisorba, by the pink filaments of Plantago, and by the yellow anthers in the Sallow willow" (p. 271).
"The interpretation, then, I would offer of inconspicuousness and all kinds of degradations is the exact opposite to that of conspicuousness and great differentiations; namely, that species with minute flowers, rarely or never visited by insects, and habitually self-fertilised, have primarily arisen through the neglect of insects, and have in consequence assumed their present floral structures" (p. 282).
In a letter just received from Mr. Henslow, he gives a few additional illustrations of his views, of which the following are the most important: "Passing to Incompletae, the orders known collectively as 'Cyclospermeae' are related to Caryophylleae; and to my mind are degradations from it, of which Orache is anemophilous. Cupuliferae have an inferior ovary and rudimentary calyx-limb on the top. These, as far as I know, cannot be interpreted except as degradations. The whole of Monocotyledons appear to me (from anatomical reasons especially) to be degradations from Dicotyledons, and primarily through the agency of growth in water. Many subsequently became terrestrial, but retained the effects of their primitive habitat through heredity. The 3-merous [sic] perianth of grasses, the parts of the flower being in whorls, point to a degradation from a sub-liliaceous condition."
Mr. Henslow informs me that he has long held these views, but, as far as he knows, alone. Mr. Grant Allen, however, set forth a similar theory in his _Vignettes from Nature_ (p. 15) and more fully in _The Colours of Flowers_ (chap. v.), where he develops it fully and uses similar arguments to those of Mr. Henslow.]
[Footnote 156: H. Müller gives ample proof of this in his _Fertilisation of Flowers_.]
[Footnote 157: _Cross-and Self-Fertilisation_, p. 27.]
[Footnote 158: _Animals and Plants_, vol. ii. p. 145.]
[Footnote 159: Müller's _Fertilisation of Flowers_, pp. 448, 455. Other cases of recent degradation and readaptation to insect-fertilisation are given by Professor Henslow (see footnote, p. 324).]
[Footnote 160: _The Colour Sense_, by Grant Allen, p. 95.]
[Footnote 161: _The Colour Sense_, chap. ix.]
[Footnote 162: See _Origin of Species_, sixth edition, p. 220.]
