494 



STRUCTURE AND LIFE HISTORIES 



tains endosperm, with the embryo located at one side 

 (Figs. 378 and 83). The cotyledon {sciitellum) serves to 

 secrete enzymes that digest the endosperm, and then 



Fig. 378.-Longitudinal section of a grain of wheat {Triticum vulgare), 

 p.s.c, pericarp and seed-coats (united); en, endosperm; al, aleurone layer; 

 gl, glandular layer of the scutellum; sc, scutellum; sp, sheath of plumule 

 {coleoptile); pi, plumule; r.cot., rudimentary cotyledon; ra, radicle; re, 

 root-cap; r.s., root-sheath (coleorhiza). (From microscopical preparation 

 of E. W. Olive.) 



absorb the digested food by osmosis (Fig. 62). The cylin- 

 drical stems are jointed and usually hollow (except at the 

 joints) . The leaves are usually long, slender, and pp.rallel- 



