CH. IX] DIVERGENCE OF VARIATION 83 



we do find. If we draw up a key to the Ranunculaceae, dealing 

 only with the seven big genera given in the list above, it will be 

 found to be just such a divergent key, so that to place a species 

 in its proper genus is a very simple matter. Here is the whole 

 key: 



A. Ovules on both sides of ventral nerve of carpel: follicle — 



Flower with 2 or (2) honey-leaves: 

 Honey-leaves sessile, odd leaf of 



perianth spurred, projecting. Delphinium 



Honey-leaves stalked, odd leaf 



helmet-shaped, erect. Aconitum 



Flower with 5 honey-leaves. Aquilegia 



B. Ovule solitary at base of ventral nerve: achene — 



Ovule with one integument. 

 Ovule pendulous: 



Leaves opposite. Clematis 



Leaves alternate (exc. involucre). Anemone 



Ovule erect. Ranunculus 



Ovule with two integuments. Thalictrum 



The key is a very simple affair, with widely divergent charac- 

 ters at every stage, so that there can be no difficulty whatever in 

 placing any species in its genus, were these the only genera in 

 the family. It is only when the smaller genera are included that 

 anv difficultv is found. With each new one that is added, the 

 characters that have to be used become more numerous and more 

 complicated. These seven large genera cover practically the whole 

 range of variation that is found in the family, to say nothing of 

 including 87 per cent of the whole, and the rest of the genera 

 come within, or very close to, the range thus indicated. If one 

 add to the seven large genera the rest of the family, which con- 

 sists of small genera not exceeding twenty species, one finds that 

 the steps which in the above key lead only to Ranunculus lead 

 also to Myosurus, Oxygraj^his, Trautvetteria, and Hamadryas. 

 A whole series of new steps in identification is now required, but 

 the important and interesting point is that all the new additions 

 come within the original key, or very nearly so. The new additions 

 that have to be made to the lists of characters are all at the 

 generic end of the key or close to it, with few exceptions. Instead 

 of finding that '"ovule erect" leads straight to Ranunculus, we 

 have to have a supplementary key like the following: 



6-2 



