150 ANTHOCYANINS AND GENETICS 



and cream. In main outline a similar series, brown or crimson, purple 

 or magenta, deep yellow and pale yellow is shown by Zinnia elegans, 

 and also by the new varieties of the Sunflower, Helianthus annuus 

 (Cockerell, 602, 603, 611). Variation in the Garden Nasturtium 

 (Tropaeolum majus) is on the same lines as in Cheiranthus, though it 

 differs in one respect, namely that in Cheiranthus the type anthocyanin 

 is purple and gives rise to a red variety, while in Tropaeolum the type 

 anthocyanin is scarlet, or carmine red, and gives rise to a purple variety. 

 The colour representing the original type of Tropaeolum is the orange- 

 red due to carmine anthocyanin on yellow plastids. A deep yellow 

 variety is the albino after the loss of anthocyanin and, as in the case 

 of Cheiranthus, it produces several pale yellow varieties approaching to 

 cream as a result of the loss of some factor from the plastids. On this 

 pale yellow ground the red anthocyanin appears as carmine or ruby. The 

 red anthocyanin also varies to a blue-red or purple, which, on the deep 

 yellow plastids, appears as maroon, and on the pale yellows as purple. 

 There is additional variation caused by anthocyanin blotches at the base 

 of the petals ; these may be carmine or purple, and may be retained when 

 the main part of the flower is free from anthocyanin ; they may, however, 

 be entirely lost, so that the flower is wholly yellow. Variation in Salpi- 

 glossis sinuata is also in all probability on similar lines to Cheiranthus. 



We may next consider an additional range in the plastid-yellow 

 series due to complete loss of colour from the plastid. In this way a 

 white arises and it may exist as such, or anthocyanin may be present 

 on the white ground. Typical of this series is Chrysanthemum ; the type 

 was in this case yellow, probably slightly tinged with anthocyanin. 

 Loss of an inhibiting factor (see p. 152) would give rise to a crimson 

 variety, i.e. purple anthocyanin on yellow plastids. Loss of yellow 

 plastids, without loss of anthocyanin, gives purple, purplish-red or 

 magenta ; loss of anthocyanin gives either yellow or white. The series 

 is then : crimson, magenta, yellow and white. Helianthemum vulgare 

 (Rockrose), Viola tricolor (Pansy) and the garden Tulips probably 

 come into the Cheiranthus-Chrysanthemum class, but our knowledge of 

 these species is not very systematic. Viola tricolor possibly contains 

 species-crosses. We can readily distinguish two groups of the garden 

 Pansy : one includes white, reddish-purple, purple and purple-blue ; 

 the other yellow, brown and crimson. But we have no evidence as 

 to how the groups are related. 



We can thus differentiate two groups or series, soluble-yellow and 

 plastid-yellow : in the former the type is generally magenta and gives 



