472 



THE AMERICAN NATURALIST [Vol.L 



types are practically the same, there being an average of 

 45 species per genus in the former and 46 in the latter. 

 This of course pulls the general averages together. The 

 more scattering distribution of trees and shrubs, however, 

 is made evident by the fact that of small genera (10 spe- 

 cies or less) they possess 3,115, as compared with 1,890 

 for herbs. 



The two types are somewhat more diverse in the num- 

 ber of genera per family. In an analysis to determine 

 this distribution, only land plants of normal growth- 

 habit were considered. The Balanophoraceae, Rafflesi- 

 aceae, Hydnoraceae, Lennoaceae and Cynomoriaceae were 

 excluded as aberrant; and families characteristically 

 aquatic were also omitted, since from their uniformity of 

 environment or other reasons unknown they are notori- 

 ously poor in generic types. Two hundred and twenty- 

 four families of dicotyledons enumerated in the seventh 

 edition of Engler's "Syllabus" remain to be considered; 

 130 of these are exclusively woody, 60 have both woody 

 and herbaceous members, and only 34 are exclusively her- 

 baceous, 4 making it evident at a glance that woody plants 

 have much the wider taxonomic distribution. In the 190 

 families which include trees and shrubs, there are just 

 4,000 genera, an average of 21 per family. In the 94 fam- 

 ilies which include herbs, there are 2,590 genera, an aver- 

 age of 27.5 per family. (The 180 "mixed" genera were 

 left out in this count. ) The f a.ct that the bulk of genera in 

 both are massed in a few large families again pulls the 

 averages together ; but the more scattering distribution of 

 woody genera over a large number of small families is 

 decidedly emphasized when we note that there are no less 

 than 39 monogeneric families of trees and shrubs, but only 

 7 of herbs (exclusive of aquatics). Of families with 5 

 genera or less there are among woody plants 83, among 

 herbs only 24. In number of species per family the differ- 



* Families like the Banunculaceae, Papaveracese, Crassulaceae, Geraniace® 



counted as strictly herbaceous; and others like the Sapindacese, AraliaceK 

 and Bignoniaceae, in which there are very few herbs indeed, have been 

 counted as strictly woody. 



