This section is from the book "On British Wild Flowers Considered In Relation To Insects", by John Lubbock. Also available from Amazon: Nature Series On British Wild Flowers Considered In Relation To Insects.
This order contains two British genera, Linum, and Radiola; the former is the well-known flax, the latter a minute erect annual, which grows on heaths and sandy places. The genus Linum contains five British species, which differ considerably in the size of their flowers, from the beautiful, blue, common flax, to the minute L. catharticum, the petals of which are but little longer than the calyx, and which yet secretes honey, from five minute glands situated on the outer side, and near the base of the five stamens. It is therefore, in spite of its minute size, frequently visited by insects, though in their absence it is capable of self-impregnation. So far as has been hitherto observed L. usitalissimum, though differing so much from L. catharticum in the size of the flowers, agrees in general arrangement, and is also capable of self-fertilisation.
The crimson L. grandiflorum, on the contrary, as Mr. Darwin has shown (Jour. Linn. Soc, Feb. 1863) presents two forms, which occur in about equal numbers, and differ little in structure, though greatly in function. In the one form, the column formed by the united styles and the short stigmas, is about half the length of the whole pistil in the other or "long-styled " form. The stigmas also of the short-styled form diverge greatly from each other, and pass out between the filaments of the stamens, thus lying within the tube of the corolla, while in the long-styled form the elongated stigmas stand nearly upright, and alternate with the anthers.
By a series of careful and elaborate experiments Mr. Darwin has shown that this species is almost entirely sterile with pollen of its own form. He repeatedly placed pollen of long-styled flowers on the stigmas of the same kind, and pollen of short-styled flowers on stigmas of shott-styled flowers, but without effect; while if pollen of a long-styled flower is placed on a short-styled stigma, or vice versa, abundance of seed is produced. In short, the pollen of the L. grandiflorum is differentiated, with respect to the stigmas of all the flowers of the same form, to a degree corresponding with that of distinct species of the same genus, or even of species of distinct genera.
Linum perenne is also dimorphous, and the difference between the two forms is more conspicuous.
Fig. 43. - Malva sylvestris.
Fig. 44. - ` rotundifolia
Fig. 45. - Stamens and stigmas of Malva sylvestris.
Fig. 46. - Ditto of Malva rotundifolia.
Of this order we have three British genera, Lava-tera, Althaea and Malva, with respectively one, two, and three specific forms. In the intoductory chapter, I have already called attention to the structure of the Mallow, with especial reference to the differences existing between Malva sylvestris (Figs. 43 and 45) and M. rotiindifolia (Figs. 44 and 46). The honey glands are five in number, at the base of the flower. Althaea and Lavatera are said to agree in general structure with Malva.