Chap. XXV. CORRELATED VARIABILITY. 331 



tinctoria. According to Spinola and others, 41 buckwheat (Poly- 

 gonum fagopyrum), when in flower, is highly injurious to white 

 or white-spotted pigs, if they are exposed to the heat of the 

 sun, but is quite innocuous to black pigs. According to two 

 accounts, the Hypericum crispum in Sicily is poisonous to white 

 sheep alone ; their heads swell, their wool falls off, and they 

 often die ; but this plant, according to Lecce, is poisonous 

 only when it grows in swamps ; nor is this improbable, as 

 we know how readily the poisonous principle in plants is 

 influenced by the conditions under which they grow. 



Three accounts have been published in Eastern Prussia, of 

 white and white- spotted horses being greatly injured by 

 eating mildewed and honeydewed vetches ; every spot of skin 

 bearing white hairs becoming inflamed and gangrenous. The 

 Eev. J. Eodwell informs me that his father turned out about 

 fifteen cart-horses into a field of tares which in parts swarmed 

 with black aphides, and which no doubt were honeydewed, and 

 probably mildewed ; the horses, with two exceptions, were 

 chestnuts and bays with white marks on their faces and 

 pasterns, and the white parts alone swelled and became angry 

 scabs. The two bay horses with no white marks entirely 

 escaped all injury. In Guernsey, when horses eat fool's 

 parsley (JEthusa cynapium) they are sometimes violently 

 purged ; and this plant " has a peculiar effect on the nose 

 " and lips, causing deep cracks and ulcers, particularly on 

 " horses with white muzzles." 42 With cattle, independently 

 of the action of any poison, cases have been published by 

 Youatt and Erdt of cutaneous diseases with much consti- 

 tutional disturbance (in one instance after exposure to a hot 

 sun) affecting every single point which bore a white hair, but 

 completely passing over other parts of the body. Similar 

 cases have been observed with horses. 43 



41 This fact and the following cases, eating buckwheat ; whilst black or 



when not stated to the contrary, are dark-woolled individuals are not in 



taken from a very curious paper by the least affected. 

 Prof. Heusinger, in ' Wochenschrift 42 Mr. Mogford, in the ' Veteri- 



fiir Heilkunde,' May, 1846, s. 277. narian,' quoted in 'The Field,' Jan. 



Settegast (' Die Thierzucht,' 1868, p. 22, 1861, p. 545. 

 39) says that white or white-spotted i3 ' Edinburgh Veterinary Journal, 



sheep suffer like pigs, or even die from Oct. 1860, p. 347. 



