40 Colours of Plants [ch. 



two whites, but on the analogy of the Sweet Pea such a result may be 

 attainable. Otherwise the same rules apply generally. At least two sets of 

 pigments take part in coloration of seed-coats : (i) brown, (2) purple. White- 

 flowered plants have seed-coats unpigmented, and the bicolour flowers go 

 with parti-coloured half-white seeds. The development of purple in the 

 coats and the pattern in which it is deposited depend on various factors 

 which can be carried by the albino. Various complications were met with 

 (see originals). The cross between the two species showed some degree of 

 sterility. 



Similar results were obtained by Emerson (120, 121). The seed-coats 

 of heterozygous plants in some cases were distinguishable. He also found 

 green pods dominant to yellow pods (cp. Ptsmn, p. 14). 



Further facts^ with a scheme elucidating some of the curious ratios 

 which the seed-colours may exhibit {e.g. 18 : t8 : 6 : 6 : 16) in F2, are 

 given by Shull (242). 



Phyteuma Halleri (dark violet) x P. spicatum (white) gave two types in 

 ^i> 5 plants being bright blue with violet tinge, 4 violet (Correns, 70). 



Pisum (Edible Peas). Flower-colours of three types, (i) Purple. 

 Standard a pale purplish white ; wings deep chocolate purple. (2) Pink. 

 Standards pinkish white; wings a fine salmon-pink. (3) White. P^ 

 containing all three types is the usual 9:3:4 in order named. Mark in 

 axils of leaves, if present, is purple in (i), red in (2), absent in whites. 

 Tschermak experimented with a purple strain without the axil-mark, and 

 found that, as in Sweet Peas, the factor for that character can be carried by 

 the albino. 



Seed-coats colourless or greenish in white-flowered plants. In plants 

 with coloured flowers one or more of three distinct kinds of pigments always 

 present: (i) a purple, occurring in spots, (2) a brown, distributed either 

 generally over the surface, or in bands (as in Maple peas), (3) an insoluble 

 greenish grey, distributed over the whole testa. Neither (i) nor (2) can be 

 developed in the absence of (3), but traces of (2) may sometimes be seen 

 in white-flowered plants. There are separate factors for (i), (2), and (3), 

 of which (i) and (2) may be carried by the whites (Lock, 176). 



Cotyledon-colours are yellow, and green. Yellow is a dominant, and 

 heterozygotes are indistinguishable from homozygous dominants. In rare 

 cases green has been seen as exceptions in Fx-, but these are probably 

 due to abnormal conditions. Many modern varieties have cotyledons 

 patched with green and yellow. Genetically these are greens which show 

 a special liability to bleaching. If protected while ripening they remain 

 green. 



Colours of Pisum have been chiefly studied by Mendel (195); Tscher- 

 mak (269, 271-3); Correns (60); R.E.C. (20); Lock (172, 173, 175-6); 

 Hurst (155). 



Poleino7iiu7n. Correns (70) found the white var. of P. coericleum 

 dominant to the yellow of P. flavum ; and the blue type oicoeruleum ^fiavum 

 gave F^ blue. It may be inferred that the yellow of flavum is a chromo- 

 plast colour, and that the blue anthocyan dominated as usual. Hybrids 

 sterile. 



Primula. P. Sinensis exists in a long series of colour-types the 

 relations of which are still being investigated by R. P. Gregory in con- 



