158 A TEXT-BOOK OF GRASSES 



genera and allied genera into higher groups without com- 

 mitting ourselves as to how the various groups came to 

 be what they are. The modem tendency is toward a 

 grouping of species in all large genera. Some of these 

 groups are recognized under the formal titles of sub- 

 genera, sections and subsections. But it is often con- 

 venient to form smaller groups centering aroxmd well- 

 known or widespread species. 



Ascherson and Grabner bring together closely allied species 

 under the heading Gesammtart (Syn. Mit.-Eur. Fl.). In our recent 

 revision of the North American Species of Panicum (Contr. U. S. 

 Nat. Herb. 15) these minor groups or species were indicated by the 

 plural of the leading species, e.g., the aUies of Panicum dichotomum 

 were grouped under Dichotoma. 



