124 TEST CASES [ch. xi 



means of selection, but quite simple by mutational differentia- 

 tion. 



In the Caryophyllaceae, all otherwise dry-fruited (usually 

 capsules), Cucuhalus alone, with one species in Europe and Asia, 

 has a berry. In Ranunculaceae, admittedly a very old and widely 

 dispersed family, Actaea has a berry, while in Annonaceae all have 

 berries but Anaxagorea. 



In Myrtaceae, half the family, the Leptospermoideae, have a 

 dry fruit, the other half, the Myrtoideae, a berry. How did 

 natural selection, working upon the ancestors, ensure that all 

 those with the berry should be more closely related to each other 

 than to those with the dry fruit? Again "tendencies" have to be 

 called in, but the differentiation answer is simple; an early 

 mutation split off a genus with a berry from one with a dry fruit, 

 and the descendants have inherited one or the other. An excep- 

 tion like Cucuhalus is explained by a later mutation which in- 

 volved a change of the chief fruit character of the family. 



A great difficulty is to explain why the berry is always the 

 same in its general structure, though it must have been picked 

 out upon so many separate occasions. Why is it usually associated 

 with the capsule, while the drupe is usually associated with the 

 achene or the nut? In some families both may be found, but each 

 keeps strictly to its own morphology, though under selection one 

 would have expected more variety. How did capsules and other 

 kinds of dry fruits that occur in close relatives all manage to 

 change to berries of the same morphological construction? No 

 intermediate forms occur, with few and slight exceptions. It is 

 clear that the phenomena of berries are better explained by 

 differentiation. 



TEST CASE XV. ACHENES AND FOLLICLES 



Here again are types of fruit found all through the classification 

 of the flowering plants. Alismaceae have achenes, while their 

 near relatives the Butomaceae have follicles. Half of the Ranun- 

 culaceae have one, half the other. Two of the three groups of 

 Spiraeoideae have one, one the other. How were all these groups 

 produced by natural selection with gradual adaptation? The 

 question has hardly been properly thought out. How did the one 

 fruit obtain, by this method, a completely closed wall, the other 

 (when ripe) a completely open one? The value of selection would 

 become less and less marked as the fruit approached perfection 



