12 с. H. Ostenfeld and Andr. Ltndager. 



The material of Aira brought home by the Danmark Expedition 

 is very interesting in many points. Some of the numbers (1283, 

 1287, 1609, 1620) answer well to A. caespitosa, var. arctica as H. G. 

 Simmons regards it, and must bear that name. It is a low, but 

 rather coarse plant, wdth short, often somewhat involute leaves, and 

 coarse more or less inflated sheaths, those of the culms bearing 

 sometimes very short blades, sometimes almost none (see PI. I and 

 PI. II, fig. 1). 



Trinius (Sp. Gram. icon, et descript.. Ill, 1836, Petropolis, PL 

 256, A et В) has given very good figures of this plant, and his 

 analysis of the spikelet (PI. 256, 1—3) is also correct. The glumes 

 are shorter than or nearly as long as the spikelet, with tips bitten 

 off; awns about as long as the pales. 



Besides this variety the Danmark Expedition has collected an- 

 other still more aberrant form of the caes/)z7osa-group which must 

 be referred to : — 



25 b. A. caespitosa L. var. pumila Ledeb., Fl. Ross., IV, 1853, 

 p. 422; A. brevifolia Nathorst, Öfv. К. Sv. Vet. Akad. Förh., 1884, 

 p. 27; A. flexuosa, var., Simmons, I.e., 1906, p. 175, et ibid., No. 16, 

 1909, p. 105. 



Trinius (1. c, PI. 256, C) has given a description and a rather 

 good illustration of it, based upon a specimen from Kamtchatka, 

 and Simmons (1. c.) describes its habit and characters very well. 



Trinius's description runs as follows: — Fig. С plantulam 

 depingit pumilam, caespites densissimos formantem, panicula parva, 

 angusta, foliis angustissimis, nunc planiusculis nunc fere capillaceo- 

 involutis, brevissimisque insignem, spiculis vero omnino cum A. cae- 

 spitosa communi congruentem. 



It forms dense mats or tufts with numerous very thin, often 

 involute and setaceous leaves, which are much softer than those of 

 var. arctica; the culms are low, but generally longer than the leaves; 

 the culm leaves are almost without blade, and with large sheaths (see 

 PI. 11, fig. 2 and PI. III). The branches of the panicle are thin and usually 

 not so contracted as in var. arctica. The glumes are long and acute, 

 as long as or nearly as long as the spikelet, not while-membraneous in 

 the margins; awns about as long as the pales, straight or slightly twisted. 



In many of its characters it comes near A. flexuosa L., but 

 I cannot follow Simmons when he regards it as a form of that 

 species; the characters of the spikelet, especially of the awns makes 

 it a necessity to refer it to the caespz7osa-group, and I follow Ledebour 

 and Trinius in this point. It appears always to grow along the 

 margins of ponds or of tarns, and perhaps some of its peculiar cha- 

 racters are adaptations to the habitat. 



