Chap. XXV. CORRELATED VARIABILITY. 325 



remarkable change in form and nature which the fruit under- 

 goes during its development. 



In the following instance we have the colour and the form 

 of the petals apparently correlated, and both dependent on 

 the nature of the season. An observer, skilled in the subject, 

 writes, 31 " 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 of the flower are very 

 inconstant, and during certain years some, or even all the 

 flowers, become uniformly coloured; and it has been observed 

 with several varieties, 32 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 

 connection ; but I will now give cases in which we can- 

 not even conjecture, or can only very obscurely see, the 

 nature of the bond. Isidore Geoflroy Saint-Hilaire, in his 

 work on Monstrosities, insists, 33 " 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 in a rare affection of the 

 renal capsules (of which the functions are unknown), the 

 skin becomes bronzed ; and in hereditary syphilis, as I hear 

 from Sir J. Paget, both the milk and the second teeth 

 assume a peculiar and characteristic form. Professor Rol- 

 leston, also, informs me that the incisor teeth are sometimes 



31 'Gardener's Chron.,' 1843, p. p. 402. See also M. Camille Dareste, 

 877. ' Recherches sur les Conditions,' &c. 



32 Ibid., 1845, p. 102. 1863, pp. 16, 48. 

 23 ' Hist, des Anomalies,' tom. iii. 



