13 



I. 



7. Palea distinctly 3-uui-vecl iu one spikelet, the mid-uerve as prominent a.s the 

 Jieels but not reacliing the apex; iu this case the prolongation of the rachiUa unusu- 

 ally well developed ( C. breviscia). Palea 5-uerved in one specimen, the nerves nearly 

 equidistant and equally prominent to near the apex, rjut only the normal keels quite 

 reaching the apex, the palea being strongly grooved only near the base and the 

 strongly developed prolongation of the raehilla slightly lateral ; iu other spikelets 

 the two outermost nerves anastomosing with the normal keel nerves and the central 

 one disappearing below the middle of the palea (C. aleiitica). 



The frequency of two-tlowered spikelets iu this genus, often when the plant is 

 apparently quite healthy, shows how slight the dividing line between the tribes 

 Agrostided' aud Jvtnew may become. 



HYBRIDISM. 



To what extent the species of CalamagTostis hybridize with oue 

 another, if at all, can only be detenuiued by actual experiment or the 

 closest kind of field observation. It is not improbable that natural 

 hybrids occur in the genus. Apparent crosses of C. liyperhorm with 

 C. imrpuraseens, C. hyperhorea with G. langsdorffii and C. canadensis 

 with C. sulsdorjii, are represented in the United States National Herb- 

 arium. 



SPECIES EXCLUDED. 



Calamaf/rostis (lujantea 2^utt., Trans. Am. Phil. Soc. (II) 5: 143 

 {lS31)-=CaI<(nioi-i{fa lonyifolia (Hook.) Scribn. 



Calamagrostis andina Nutt. PI. Gamb., Journ. Acad. Phila. (II) 1: 

 187 (1818), not identifiable from the description, but certainly not a 

 Calamagrostis. 



Agrosfis a'qnivalvis Trin., referred to Beyeuxia by Bentham on account 

 of the minute usually hairy prolongation of its raehilla, is iu all other 

 respects an Agrostis and should be retained iu that genus. 



NORTH AMERICAN SPECIES OF CALAMAGROSTIS. 



ANALYTICAL KEY TO THE SPECIES. 



1. Awn strongly geniculate, exserted, callus hairs shorter than the flowering glume 

 2 



1. Awn straight or nearly so, included, callus hairs not nuuh shorter than the 



flowering glume 24 



2. Awn much exceeding empty glumes 3 



2. Awn shorter than or not much exceeding empty glumes 11 



3. Panicle loosely flowered, rays spreading 4 



3. Panicle densely flowered, rays appressed 8 



4. Plants not c;espitose 5 



4. Plants sti'ongly Cipspitose 6 



5. Tall (5 to 14 dm. high), flowering glume strongly granular-scabrous 



1. C. bolanderi. 



5. Low (1.5 to 3 dm. high), llowering ginmc scabrous, but not granular 



2. C. deschanipsioides. 



6. Leaves of innovations short, not nearly equaling the dark purple panicle, plant 



soft 7 



