204 
Willis .— Age and Area. 
not necessarily happen with a hollow curve. The fact that the logarithmic 
curve is a straight line (Figs. 2, 3) indicates that the genera have been 
formed by a close approximation to the rule of compound interest, a con¬ 
clusion which has very important consequences, to which I shall refer in 
later publications. 
Fig. 1. Hollow curves exhibited by the grouping into sizes of the genera in the first 
fifteen largest families of flowering plants. Each curve is diagonally above the preceding one, 
as indicated by the heavy black dots (points of origin). Note that the curve almost always turns the 
corner between the point marking the number of genera with 3 species, and that marking the number 
with 5 (indicated by the dotted lines). The number after the name of the family shows the number 
of genera in it. 1 
Mr. Tate Regan quoted the case of the names in the London Telephone 
Directory as giving a hollow curve like the plants, evidently thinking that 
there was no rule which governs the origin of names, and that they showed 
no distribution like plants. The answer to this criticism has been made 
very easy by the existence of a book of which Mr. Tate Regan was evidently 
1 Fig. 1 is reproduced by permission from Willis ( 11 ) ; the block kindly lent by the Syndics of 
the Cambridge University Press. 
