LAMSON-SORTBNER AND MERRILL— GRASSES OF ALASKA. 49 



SYSTEMATIC TREATMENT. 

 I»( ) A CEAE (Grasses. ) 



Fibrous-rooted, annual or perennial, herbaceous (rarely woody) plants, with usually 

 hollow, cylindrical (rarely flattened), and jointed stems (culms), the internodes for 

 more or less of their length enveloped by the sheath-like basal portion of the two- 

 ranked and usually linear, parallel-veined leaves; flowers without any distinct peri- 

 anth,* hermaphrodite or rarely unisexual, solitary or several together, in spikelets, 

 which are arranged in panicles, racemes, or spikes; spikelets consisting of a short- 

 ened axis (the rachilla) and two or more chaff-like, distichous, imbricated bracts 

 (glumes), of these the first two, rarely one or none or more than two, empty (empty 

 glumes); borne in the axil of each of the succeeding bracts (excepting sometimes the 

 uppermost) a flower (the bracts hence named flowering glumes or lemmas); opposed 

 to each lemma, with its back turned toward the rachilla, usually a two-nerved, two- 

 keeled bract or prophyllum (the palea), this frequently enveloping the flower by 

 its infolded edges; at the base of the flower, between it and its glume, usually two 

 very small hyaline scales (lodicules), with rarely a third lodicule between the 

 flower and the palea; stamens, usually three (rarely two or one, or more than three), 

 with very slender filaments and two-celled, usually versatile, anthers; pistil with a 

 one-celled, one-ovuled ovary, and one to three, usually two, styles, with variously 

 branched, most frequently plumose, stigmas; embryo small, lying at the front and base 

 of the seed, covered only by the thin pericarp; fruit a caryopsis, rich in albumen. 



The characters employed in defining the tribes and genera are usually those pre- 

 sented by the spikelets or inflorescence. While the characters of the order an- well 

 defined the establishment of the several subdivisions is very difficult, and in no case 

 can be based upon a single character, but only upon a combination of them. There is 

 no one tribe or large genus which can be separated absolutely from all others, there are 

 always exceptions or intermediate forms connecting them, and the same statement is 

 largely true of many of the species, especially in the genera Poa and Festuca. 



KEY TO THE TRIBES AND GENERA. 



Spikelets distinctly pedicellate, racemose or paniculate; 

 panicles sometimes contracted and spike-like. 

 The first and second florets in each spikelet sfami- 



nateor imperfect Tribe I. PHALARIDEAE. 



The lowest florets perfect, the imperfect flowers, if 

 any, uppermost. 



Spikelets one-flowered Tribe II. AGROSTIDEAE. 



Spikelets two to many-flowered. 



Lemmas awned on the back; glumes longer 



than the lemmas Tribe III. AVENEAE. 



Lemmas awnless or with a terminal awn, 

 glumes usually shorter than the lemmas. Tribe V. FESTUCEAE. 

 Spikelets sessile in spikes. 



Spikes unilateral Tribe I V. CHLORIDEAE. 



Spikes not unilateral Tribe VI. HORDEAE. 



Tribe I. PHALARIDEAE. 



Glumes nearly equal, scarcely exceeding the lemmas, which 



are awnless or very short-awned 1. Savahtana. 



