INTEODUCTION. 13 



amounts to saying tliatj at that time, about half the number 

 were synonyms. In the ' Genera Plantarum ' of Bentham 

 and Hooker, fascicles 1 and 2, published in 1862 and 1865, 

 comprising almost the same series of Orders, I found, by 

 making the same approximative calculation,' 117 synonyms 

 for 100 accepted genera. It would seem, then, that the 

 proportion of generic synonyms has been doubled in thirty- 

 six years. 



That this increase will long continue in the same ratio 

 does not seem at all probable. As we become acquainted 

 ■v?ith a larger number of species, it is found more easy to 

 group them naturally, to say nothing of our resources for 

 analysis, which are better than they were formerly, nor of 

 the general improvement of descriptions. For the last forty 

 years a great number of genera have been made from defec- 

 tive materials, but this will be less common henceforth ; be- 

 sides which, we are drawing near the limits of discovery in 

 point of genera. In every fresh volume of the ' Prodromus,' 

 I remark a decrease in the proportion of new genera. There 

 are Orders in which the number of genera hardly varies. 

 Lindley, in 1853, estimated the number of genera of Ewphor- 

 hiacecB at 191 ; and it so happens that, in the recent mono- 

 graph of M. Boissier and Dr. Miiller (Prodr. xv, sect. 2), it 

 is precisely 191. I have shown elsewhere^ that the mean 

 geographical area of genera is about ^-f „■ of the solid surface 

 of the globe. Notwithstanding the exceptional smallness 

 of certain areas, it may be supposed that collectors have 

 now crossed most of the countries occupied by each genus, 

 and that we are thus pretty nearly acquainted with aU ex- 

 isting genera. Surely nothing is more uncommon nowa- 

 days than the proposal — and, above all, the admission — of 

 a new genus in the floras of the northern hemisphere, with- 

 out the tropics. For some time longer we shall see genera 

 remodelled, — genera will frequently be formed into sections, 

 or vice versa ; but, if we may judge from European floras, 



' Taking letters A and B of the same index, comprising pretty nearly 

 the same Orders. 



' ' G^ographie botanique raisonnee,' p. 1142. 



