THE EVOLUTION OF THE FLOWERS 75 



The cold of the Chalk Period gave them their oppor- 

 tunity. Then, as we saw, the flowering trees and 

 plants spread from eastern America, which seems to 

 have been higher than the west, and over the whole 

 northern hemisphere. There was still land across 

 the northern Atlantic, and in the very slow way of 

 forests they gradually reached and overran Europe. 

 Not only the trees I named, but the oleander and 

 magnolia, the palm and the grass, the lily and orchis 

 and iris, now came upon the stage. From green the 

 earth had turned partly yellow. From yellow it now 

 turns white. 



As flowers are not fossilized, one is often asked how 

 we know that there were these successive waves of 

 colour. It is, of course, an inference; but it has good 

 grounds. If you arrange a large number of flowers 

 according to their degrees or stages of organization — 

 according to the complexity or simplicity of their 

 seed organs, petals, and sepals — you will find a pro- 

 nounced colour scheme. The simplest are predomi- 

 nantly yellow (green at first). Those of the next 

 stage of organization are mainly white, with some red. 

 The colour red predominates in the next group ; and 

 at the top you get blue and variegated flowers. As 

 this corresponds with their evolution in time, the sim- 

 plest naturally coming first, we gather the successive 

 appearances of the colours in nature. 



It may also be asked how we can read the change 

 of climate from the appearance and trivimphant 



