THE MONOCOTYLEDONES 2079 



10. Stipeae. Annual or perennial herbs with rough, rigid stems and 

 narrow leaves. Spikelets hermaphrodite, one-flowered, arranged 

 in open or contracted panicles. Axis of the spikelets disarti- 

 culating above the glumes. Glumes mostly persistent, one or 

 both longer than the floret. Outer paleae mostly terete with 

 convolute or involute margins, becoming rigid and indurated 

 at maturity; three- to seven-nerved, with nerves close together 

 at the apex. Awned from the centre or from the minutely two- 

 lobed tip. Awn simple or divided into three branches. Lodicules 

 two or three. Stamens three. Fruit a caryopsis, tightly 

 embraced between inner and outer paleae. 

 The tribe is a small one, containing some eight genera which are 

 distributed mostly in tropical and subtropical regions. Some are found in 

 warm temperate regions. The best-known genera are Aristida, Stipa, 

 Oryzopsis and Milium. The genus Aristida has about 160 species. Milium 

 ejfiisum is known as Millet Grass and occurs in Britain. It must not be con- 

 fused with true Millets (see p. 2082). The genus Stipa (Fig. 2015), with 



Fig. 2015. — Stipa teuacissima. Spikelet showing 

 the long, sharply flexed awns, which are 

 hygroscopic. See in text. 



120 species, occurs mainly under xerophytic conditions. S. peunata has 

 leaves which roll inwards when the air is dry. The fruit is awned, the tip of 

 the awn being feathered and hygroscopic. The fruit is thin and sharply 

 pointed with backwardly directed hairs at the tip. The awn twists and 

 untwists with variations in the moisture of the air, and the tip of the fruit, 

 if on soft ground, is driven into it, the feathers by coming into contact with 

 other objects assisting in the process. 5. tenacissima is the Esparto grass 

 from which paper is extensively made. 



