CH. IX] DIVERGENCE OF VARIATION 79 



Perianth five — four Achatocarpaceae 



Flower 5-nierous — 3-merous Limnanthaceae 



K and C alternate — superposed Caricaceae 



Corolla valvate — convolute Quiinaceae 



Corolla free — united Xyridaceae 



Stamens few — oo Salicaceae 



Carpels two — three Balanopsidaceae 



Capsule — berry Balsaminaceae 



Taccaceae 



It is clear that in these small families the first split, which is 

 only into two genera, shows just as important divergences as does 

 the first split in the large families, which is into two sub-families, 

 and the two genera of the small family are just as well separated 

 as are the two (average) largest genera of the big family, which 

 head its two chief sub-groups. The importance of this fact we shall 

 better appreciate when we return to its discussion in the Test 

 Cases (below, p. 112). If small families really consisted of relics, 

 one would not expect that their genera should be divided by 

 divergences of any special size, and certainly not that the diver- 

 gences would be of the size and forin that one expects to find 

 between the sub-families of large families, or even between the 

 large families themselves. 



If one take a number of monotypic families, or families of one 

 genus, from the first edition of Engler, and look at the distinc- 

 tions there given for dividing the species of each of the genera 

 into two chief groups, one finds these characters to be of some 

 systematic importance, and often to be characters that are not, or 

 hardly, capable of having intermediates. It is very hard to see 

 how characters of such divergence should be those supposed to 

 be left in the genera that survive of what is supposed to be a 

 dying family. Here are a few examples : 



Monocotyledons . 



Typhaceae. Fruit with longitudinal groove, and open- 



ing in water; seed not united to fruit 

 wall. 

 Fruit without groove, not opening in water; 

 seed united to fruit wall. 



Sparganiaceae. Inflorescence branched. 



Inflorescence not branched. 



Naiadaceae. Dioecious. Stem and back of leaf spiny. 



Testa of manv lavers of cells. 

 Monoecious. Stem and back of leaf not 

 spiny. Three layers. 



