LA W OF PROGRESSIVE COLOUR A TION. 43 



effected the progressive modification of the pig- 

 mentary matter. 



The Papaveracece or poppies show us somewhat 

 similar results. Many of the less developed forms, 

 with small petals, are yellow. For example, the 

 celandine, Chelidonium majus, has a very simple ovary 

 and comparatively inconspicuous flowers : and its 

 petals are of just the same primitive golden yellow as 

 those of the buttercups, the potentillas, and the rock- 

 roses. GlaMcium luteum, another little-developed 

 form, is also yellow. So are the Californian Esch- 

 scholtzias of our gardens. But in the field poppies, 

 Papaver rhczas, P. dubium, P. hybridum, &c., which 

 have extremely large and expanded petals, together 

 with a highly modified compound ovary, bright scarlet 

 is the prevailing colour, though pale red and white 

 also occur. The still larger garden poppy, P. somni- 

 ferum, is bluish white, with a purple base to the 

 petals. 



The Cruciferce are a family which display a good 

 deal of variety of colouration, though not so largely 

 within the limits of our British species. The most 

 primitive and simple forms have yellow flowers, as in 

 the case of the cabbage genus (Brassica) including char- 

 lock, mustard, and turnip ; the rockets (Barbarea and 

 Sisymbriuni) ; and the gold-of-pleasure (Camelina 

 sativa). Most of these are dry-field weeds, and they 

 have open little-developed blossoms. Their petals 

 usually fade white. In the genus Nasturtium or 

 watercress we have four species, three of which are 

 yellow, while one is white. In treacle-mustard (Ery- 

 simum\ the yellow is very pale, and the petals often 

 become almost white. Just above these earliest forms 



