112 FIRST BOOK OF GRASSES 



sort of receptacle built of certain characters and 

 open to any species having those characters. Lin- 

 nseus's idea of Cenchrus, for example, was primarily a 

 genus of bur-grasses, and, besides what is now recog- 

 nized as Cenchrus (represented by Figs. 70 and 71), 

 he included in it a species of Nazia (Fig. 54) and a 

 Mediterranean grass in which the ''bur" is composed 

 of the rigid lobes of the lemmas of the dense head of 

 spikelets, as well as a plant that is not a grass. 



This brief explanation is offered to save the begin- 

 ner undue bewilderment when he finds in using 

 different books that the standard excuse offered by 

 botanists of all times and places, that the Latin name 

 of a plant is the same throughout the world, is not as 

 true as could be wished. 



It will be noted in using botanical works that cer- 

 tain characters are accepted as generic, that is, as 

 indicating that species having these characters in 

 common belong to a single genus. Such are the 

 5-nerved keeled lemmas of Poa. Other characters, 

 sometimes quite as conspicuous, such as the pu- 

 bescence or want of it in Poa, and the presence or 

 absence of an awn in Bromus and Festuca, are re- 

 garded as specific, that is, as differentiating species. 

 It might seem as though by some revelation certain 

 characters are known to be generic and others to be 

 specific. Such is not the case. A species consists of a 

 group of individuals presimiably capable of freely 

 inter-breeding. A genus is a group of species which 

 in the sum totial of their characters are so much alike 



