2o6 Flowers and their Pedigr^ees. 



pollen, and the use of the coloured petals is, in fact, 



to attract the insects and to induce them to fertilise 



the seeds. Now, yellow seems to have been the 



original colour of the petals in almost all (if not 



absolutely in all) families of flowers ; and the greater 



number of potentillas are still yellow. But different 



flowers are visited and fertilised by different insects, 



and as some insects like one colour and some another, 



many blossoms have acquired white or pink or purple 



petals in the place of yellow ones, to suit the particular 



taste of their insect friends. In tracing the upward 



course of development in the roses, we shall see that 



they follow the ordinary law of progressive chromatic 



changes : the simpler types are yellow ; the somewhat 



higher ones are white ; the next pink ; and the highest 



in this particular family are red ; for no rose has yet 



attained to the final stage of all, which is blue. The 



colours of petals are always liable to vary, as we all 



see in our gardens, where florists can produce at will 



almost any shade or tint that they choose ; and when 



wild flowers happen to vary in this way, they often 



get visited by some fresh kind of insect which fertilises 



their seeds better than the old ones did, and so in 



time they set up a new variety or a new species. 



Two of our English potentillas have thus acquired 



white flowers to suit their proper flies, while one 



