THE GRASS FAMILY 387 



are called exogenous ' or outside-growing, because new wood 

 when formed is added on the outside of an older ring. 



143. The grass family (Graminae). Examples: oat (Fig. 1- 

 4, pages 12-14), rice (Figs. 5, 6, pages 16, 17), rye (Fig. 

 7, page 18), wheat (Figs. 8, 9, pages 19, 20), barleys (Figs. 

 10-12, pages 21, 22), maize (Figs. 13-15, pages 23, 24), 

 sugar-cane (Fig. 114, page 106), broom-corn (Fig. 222, page 

 236), and bamboo (Fig. 224, page 239). 



Formulas of Zea, Saccharinum, Andropogon, Oryza, .Avena, 

 Secale, Triticum, Hordeum, Bambusa, and Graminese are shown 

 on pages 420-423. 



The grasses introduce us to a new sub-class, characterized 

 partly, as we shall see, by having the leaf-veins running in a 

 regular, more or less parallel system. Leaves with such a 

 framework are said to be ■parallel-veined. Grass leaves always 

 have the veins running lengthwise from base to tip. 



Other noteworthy features of grass leaves are that the base 

 is wrapped about the stem so as to form a sheath the edges 

 of which overlap as shown in Fig. 13; and the blades extend 

 from only two sides of the stem, thus coming into two vertical 

 ranks. 



Most grass stems are round and hollow like straws. Rarely, 

 as in the stalk of maize, there is a solid cylinder of pith, 

 through which run scattered bundles of firmer, more or less 

 woody material, not forming true rings, but often so crowded 

 toward the surface as to constitute a somewhat bark-like 

 zone. From an erroneous idea that these scattered bundles 

 originated near the center of the stem and were forced out- 

 ward by new growth, all stems with scattered bundles were 

 early described as "inside-growing" or endogenous - — a term 

 still used conveniently, however, by way of contrast for stems 

 of seed-plants of the non-exogenous type. 



The bracts and bractlets of grasses in general are com- 

 parativety thin and stiff, hke the husks or chaff of grain, 

 and have received the special name of glumes.'^ 



1 Ex-og'en-ous < Gr. exo, outside; genes, producing. 

 - En-dog'en-ous < Or. endos, within. 



' Glume < L. glurna, husk of corn. In our formulas the glumaceous 

 character is denoted by the inverted exclamation mark as in Bj . 



