78 DIVERGENCE OF VARIATION [ch. ix 



each case, omitting a few keys where the first break is into three 

 or more. These sixty famihes of course were selected for the 

 Dictionary as being the larger or more important, and we shall 

 go on to deal with the smaller ones below. 



It will be seen at once that these are characters the bulk of 

 which are of the same rank as the "family" characters given in 

 Appendix I. To take a few examples, one finds among them such 

 character-pairs as these, which can all be matched in the family 

 characters : 



1. Leaves opposite — alternate Gentianaceae 



2. Leaves in two ranks — not Musaceae 



3. Inflorescence racemose — cymose Verbenaceae 



4. Flower naked — with perianth Betulaceae 



5. Perianth actinomorphic — zygomorphic Campanulaceae 



6. Calyx polysepalous — gamosepalous Caryophyllaceae 



7. Calyx valvate — imbricate Mimoseae (Legum.) 



8. Stamens free — in tube Meliaceae 



9. Stamens two — one Orchidaceae 



10. Carpels free — united Annonaceae 



11. Carpels six to fifteen — three to five Hydrocharitaceae 



12. Ovule one per loculus — two Euphorbiaceae 



13. Fruit a berry — loculicidal capsule — 



septicidal capsule Ericaceae 



14. Fruit many-seeded — one-seeded Myrsinaceae 



15. Fruit achene — follicle Ranunculaceae 



Incidentally, how does natural selection account for, or explain, 

 the difi'erences shown in 2, 3, 6, 7, 9, 11, 12, 13, 14, 15, to say 

 nothing of the others? 



If one go on to the second dichotomy in a key to a big family, 

 one finds that there are on the whole fewer, though still some, of 

 the "family" differences shown, but these become less frequent 

 in proportion to the total, as one goes down the list. 



It might be thought, perhaps, that small families would show 

 a diff'erence from the larger ones, possibly in having smaller 

 divergences in their classification into genera. If they were really 

 relics, as they are often supposed to be, this might be the case, 

 but in actual fact it is not found, as a glance at Appendix III will 

 show. This contains the distinguishing characters of the genera in 

 the families that contain two only. Here again one finds such 

 distinctions as: 



Leaves opposite — alternate Caryocaraceae 



Erythoxylaceae 

 Trigoniaceae 



