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DARWINISM
CHAP.
and as the chief use of these is to attract insects, they could hardly have existed in primitive flowers.[1] We know, moreover, that when the petals cease to be required for the attraction of
- ↑ 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.
