78 THE COLOURS OF FLOWERS. 



We should thus naturally expect them to be pink or 

 lilac, and this is actually the case with most of our 

 native species, the genus Epilobium having usually 

 purple or red flowers, rarely white ; while the smaller 

 Circ&as are pink or whitish. Why, then, is the even- 

 ing primrose yellow ? Because it is a night-flowering 

 plant, fragrant in the evening, and its pale yellow 

 colour makes it easily recognisable by moths. In this 

 case, however, two points mark it off at once from the 

 really primitive yellow flowers. In the first place, it 

 has not the bright golden petals of the buttercup, but 

 is rather more of a primrose tint ; and this is a 

 common distinguishing trait of the later acquired 

 yellows. In the second place, it belongs to a genus 

 in which red and purple flowers are common, whereas 

 the buttercups are almost all yellow or whitey-yellow, 

 and the potentillas mostly yellow or white, In short, 

 primitive yellow flowers are usually golden, and belong 

 to mainly yellow groups : reverted yellow flowers are 

 often primrose, orange, or dull buff, and occur 

 sporadically among blue, red, or purple groups. 



There are other cases less immediately apparent than 

 these. For instance, Lamium galeobdolon, a common 

 English labiate, belonging to a usually purple or blue 

 family, is bright yellow. But we can form some idea 

 of how such changes take place if we look at the 

 pansy, which we have seen reason to believe is 

 normally violet-purple, but which usually has a yellow 

 patch on the lowest petal. In the pansy's var. lutea, 

 the yellow extends over the whole flower, no doubt 

 because this incipient form has succeeded in attract- 

 ing some special insect, or else grows in situations 

 where yellow proves more conspicuous to bees than 



