MONOCOTYLEDONS. 303 



awned flowering-glumes; 1 and in having the flowering- glume 

 and the palea joined to the ripe grain, forming the " husk " 

 which has to be removed by grinding ; in addition to the 

 differences already noted in the inflorescence. 



317. The Grass Family (Graminaceae) is excelled in 

 number of species by the Orchid, Bean, and Composite 

 families; the known species in these four families number 

 4,000, 5,000, 7,000, and 11,000 respectively. Its success in 

 the struggle for existence, however, is shown by the fact that 

 Grasses vastly exceed all other families as regards the number 

 of individuals, and in their world- wide distribution. 



Grasses are mostly herbaceous plants, though a few tropical types 

 are woody and tree-like (e.g. Bamboos), but even the latter show no 

 secondary thickening of the stem. They are easily distinguished from 

 other grass-like plants e.g. Sedges and some Rushes by their two- 

 rowed leaves and circular or flat (in cross-section) stems ; the leaves 

 very rarely (Bamboos) have stalks, and the stems are rarely solid 

 (Maize, etc.) and rarely branch in the upper parts. Most Grasses are 

 perennial, though several (besides Wheat and Oat) are annual e.g. 

 Sea and Wall Barley, Darnel, Poa annua. Annuals are easily recog- 

 nised as such by all the shoots bearing inflorescences. Perennial Grasses 

 grow by means of buds which arise from the lowest nodes of the shoot, 

 within the leaf -sheaths. 



The general habit of the plant depends largely on the way in which 

 these buds grow out. (1) The new shoots grow up inside the leaf- 

 sheaths and the plant then forms only tufts or tussocks e.g. Sheep's 

 Fescue, Cock's-foot, Timothy, Dog's-tail ; (2) the shoots grow up in 

 the sheaths, but some or all of them later grow along the soil as 

 runners ; (3) the buds break through the leaf-sheaths and either form 

 runners (above, ground) or creeping underground stems ("stolons"). 

 Some Grasses vary in habit ; for instance, the common Bent-grass 

 (Agrostis alba) is tufted when growing on dry heaths, but has runners 

 or stolons when in rich moist soil, while there are several varieties 

 of Sheep's Fescue with stolons. Other examples of tufted (tussock- 

 forming) Grasses are Hair-grass (Aira), Mat-grass (Nardus), Bromes, 

 Rye-grasses. Yorkshire Fog and Marsh foxtail are examples of 

 Grasses with runners. Common and easily-recognised stolon-forming 

 Grasses are Couch-grass, Lyme-grass, and Marram-grass (Psamma). 



In most Grasses the leaf-sheath is split down the side opposite the 

 blade and rolled round the stem so that one edge overlaps the other, 

 but in a few cases the sheath is entire e.g. the Water-grass (Glyceria). 

 In Yorkshire Fog the prominent keel of the blade runs down as a 



1 Some varieties of Wheat ("bearded" varieties) have an awn, 

 especially in dry climates. 



