Chap. 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, 26 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 nature of the bond. 

 Isidore Geoffrey St. Hilaire, in his work on Monstrosities, in- 

 sists, 29 " 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,' torn. xx. p. 29 < Hist deg Anomalies,' torn. iii. p. 

 188 - 402. See also M. Camille Dareste, 



2 7 ' Gardener's Chron.,' 1843, p. 877. ' Recherches sur les Conditions,' &c, 



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



ft 



