Straiuberrics. 89 



trailed or crept closely along the ground would soon 

 be starved out for want of carbonic acid (the raw 

 material of growth) by their surrounding competitors. 

 In another direction the ancestors of the straw- 

 berry and of the barren strawberry also diverged from 

 their cinquefoil predecessors, and that was in the 

 peculiar colour of their flowers. For some reason 

 rather difficult to decide, the petals have changed 

 from yellow to white. Difficult to decide, I say, be- 



FiG. 18. Fi«- 19. 



Flower of Wild Strawberry. Flower of White Potentilla. 



cause we do not exactly know what are the insects 

 which the strawberries set themselves out especially to 

 please or what is the peculiar nature of their specific 

 taste. But, as a rule, this change from yellow to white 

 petals is an ordinary concomitant of higher develop- 

 ment, and it probably accompanies some change in 

 the insects to which fertilisation is generally due. 

 Our own native species have got no further in the 

 upward course of development than white ; but two 



