2078 A TEXTBOOK OF THEORETICAL BOTANY 



Botany. In A. sterilis the awns cross and when wetted they attempt to 

 untwist, thus pressing on one another until they produce a sudden fracture 

 which jerks away the separate fruits. 



i 



Fig. 2014. — Arrlienatliennii elatiiis. Cluster 

 of two flowered spikelets in anthesis, 

 showing extruded anthers, pendent on 

 their deUcate filaments and the feathery 

 stigmas. 



9. Agrosteae. Annual or perennial herbs, mostly with narrow leaf 

 blades. Spikelets usually all alike and hermaphrodite, one- 

 flowered, small and laterally compressed, borne either in open or 

 contracted or spike-like panicles. Axis of the spikelet disarti- 

 culating above the glumes. Glumes usually persistent, as long 

 as the spikelet and enclosing the flower. Outer paleae hyaline or 

 membranous, often thinner than the glumes, mostly three- to 

 five-nerved. Paleae awned or awnless, awns where present 

 arising usually from the back of the entire or two-lobed tip; 

 straight or geniculate. Stamens three, two or one. Fruit a 

 caryopsis, generally enclosed between inner and outer paleae. 

 Some forty-five genera are included in this tribe, many of which are 

 valuable fodder grasses. They occur mainly in temperate regions or in 

 mountainous regions in the tropics. Among the better-known genera 

 we may mention Agrostis, Calamagrostis, Lagiiriis, Polypogon, Phletim and 

 Alopecuriis. Of these Agrostis, with about 130 species, includes A. alba 

 (White Bent) which is a valuable pasture grass. This and Calamagrostis, 

 with 200 species, are the largest genera. 



