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Show 330 LAWS OF VARIATION. CHAP. XXV. main permanently blue and the ears would be incapable of perceiving sound ; and we should thus understand this curious case. As, however, the colour of the fur is determined long before birth, and as the blueness of the eyes and the whiteness of the fur are obviously connected, we must believe that some primary cause acts at an early period. The instances of correlated variability hitherto given have been chiefly drawn from the animal kingdom, and we will now turn to plants. Leaves, sepals, petals, stamens, and pistils are all homologous. In double flowers we see that the stamens and pistils vary in the same manner, and assume the form and colour of the petals. In the double columbine ( Aquilegia vulgaris), the successive whorls of stamens are converted into cornucopias, which are enclosed within each other and resemble the petals. In hose-and-hose flowers the sepals mock the petals. In some cases the flowers and leaves vary togethe.r in tint : in all the varieties of the common pea, which have purple flowers, a purple mark may be seen on the stipules. In other cases the leaves and fruit and seeds vary together in colour, as in a curious pale-leaved variety of the sycamore, which has recently been described in France,23 and as in the purple-leaved hazel, in which the leaves, the husk of the nut, and the pellicle round the kernel are all coloured purple.24 Pomologists can predict to a certain extent, from the size and appearance of the leaves of their seedlings, the probable nature of the fruit; for, as Van Mons remarks, 25 variations in the leaves are generally accompanied by some modification in the flower, and consequently in the fruit. In the Serpent melon, which has a narrow tortuous fruit above a yard in length, the stem of the plant, the peduncle of the female flower, and the middle lobe of the leaf, are all elongated in a remarkable manner. On the other hand, several varieties of Oucurbita, which have dwarfed stems, all produce, as N audin remarks with surprise, leaves of the same peculiar shape. Mr. G. Maw informs me that all the varieties of the scarlet Pelargoniums which have contracted or imperfect leaves have contracted flowers: the difference between 23 'Gardener's Cbron.,' 1864, p. 1202. 2 ~ V crlot gives several other instances, 'Des Varietes,' 1865, p. 72. 2fi 'Arbres .l!'ruitiers,' 1836, tom. ii. pp. 204, 226. CIIAP. XXV. CORRELATED VARIABILITY. 331 "Brilliant" and its parent" Tom Thumb" is a good instance of this. It may be suspected that the curious case described by Risso/6 of a variety of the Orange which produces on the young shoots rounded leaves with winged petioles, and afterwards elongated leaves on long but wingless petioles, is connected with the remarkable change in form and nature which the fruit undergoes during its development. In the following instance we have the colour and form of the petals apparently correlated, and both dependent on the nature of the season. An observer, skilled in the subject, writes,27 "I noticed, during the year 1842, that every Dahlia, of "which the colour had any tendency to scarlet, was deeply " notched-indeed to so great an extent as to give the petals the " appearance of a saw ; the indentures were, in some instances, " more than a quarter of an inch deep." Again, Dahlias which have their petals tipped with a different colour from the rest are very inconstant, and during certain years some, or even all the flowers, become uniformly coloured; and it has been observed with several varieties,28 that when this happens the petals grow much elongated and lose their proper shape. This, however, may be due to reversion, both in colour and form, to the aboriginal species. In this discussion on correlation, we have hitherto treated of cases in which we can partly understand the bond of connexion; but I will now give cases in which we cannot even conjecture, or can only very obscurely see, what is the natum of the bond. Isidore Geoffroy St. Hilaire, in his work on Monstrosities, insists/ 9 "que certaines anomalies coexistent rarement entr'elles, " d'autres frequemment, d'autres enfin presque constamment, "malgre la difference tres-grande de leur nature, et quoiqu'elles " puissent paraitre completement independantes les unes des '· autres." We see something analogous in certain diseases : thus I hear from Mr. Paget that in a rare affection of the 26 ' Annales du Museum,' tom. xx. p. 188. Zl 'Gardener's Chron.,' 1843, p. 877. 28 Ibid., 1845, p. 102. 29 ' Hist. des Anomalies,' tom. iii. p. 402. See also M. Camille Dareste, 'Recherches sur les Conditions,' &c., 1863, pp. 16, 48. |
