44 THE COLOURS OF FLOWERS. 



come the common small white crucifers like Cardamine 

 hirsuta, Cochlearia officinalis, and Capsella bursa- 

 pastoris. Many of these are little if at all superior in 

 organization to the yellow species, and some of them (as 

 we shall see hereafter) are evidently degenerate weeds 

 of cultivation. But such flowers as Alyssum mariti- 

 mum> with its sweet scent, its abundant honey, its 

 reduced number of seeds, and its conspicuous, 

 spreading milk-white petals, are certainly more 

 developed than small yellow species like Alyssum caly- 

 cinum. Even more remarkably is this the case in the 

 genus Iberis or candytuft, which has become slightly 

 irregular, by the two adjoining exterior petals growing 

 larger than the interior ones. They thus form very 

 conspicuous heads of bloom, obviously adapted to 

 higher insect fertilisation. Accordingly, they are 

 usually white, like our British species, /. amara ; while 

 some of the larger exotic species are a pretty pink in 

 hue. The genus Cardamine supplies us with like 

 instances. Here the smaller species have white 

 flowers, and so has the large C. amara. But in 

 C. pratensiSy the cuckoo-flower, they are usually tinged 

 with a pinkish purple, which often fades deep mauve ; 

 and in some showy exotic species the flowers are a 

 rich pink. So with Arabis : our small English kinds 

 are white; A. petrcza, with larger petals, is often 

 slightly purplish, and some handsome exotics are a 

 vivid purple. In Hesperis we get a further degree of 

 modification in that the petals are raised on rather 

 long claws ; and the flowers (represented in England 

 by H. matronalis, the dame's-violet) are a fine purple 

 and possess a powerful perfume. Closely allied is 

 the Virginia stock of our gardens, (Malcohnid) which 



