OLUMALES. 453 



it is curved entirely around the remainder of the embryo. Under prop- 

 er conditions the main root pushes througli the root sheath {ws, Figs. 

 331, 333). The plumule, consisting of a minute stem and a few rudi- 

 mentary leaves, next pushes out through the upper end of the curved 

 cotyledon (II., Fig. 333). The cotyledon remains in contact with the 

 endosperm and absorbs nourishment from it for the sustenance of the 

 growing parts. Lateral roots soon appear upon the main root, and 

 adventitious ones arise from the first internodes of the stem {w'", w", w'. 

 Fig. 833). The first leaf above the cotyledon is quite small (6), and 

 each succeeding one becomes larger and larger until the full size is 

 reached. 



In the Date the small embryo lies imbedded transversely in the large 

 endosperm. In germination the cotyledon elongates and carries the 

 enclosed root and plumule outside of the seed (//. and III., Fig. 333). 

 The apex of the cotyledon (c) expands into an organ through which 

 the dissolving endosperm is absorbed. The root pushes downward, 

 and soon develops lateral roots («)')• The plumule grows upward, es- 

 caping from the enclosing cotyledon, as shown in lY., Fig. 333. The 

 first leaves above the cotyledon are here, as in the Indian corn, much 

 less perfectly developed than the later ones. 



551. — The sub-class Monocotyledones contains about fifty 

 natural orders of plants, which are grouped into fifteen co- 

 horts. Of these only a few need be noticed. 



552,— Cohort I. Glmnales. Grass-like plants with the 

 fiowers in the axils of scales, which are arranged in spike- 

 lets ; the stamens are from one to three, rarely more ; the 

 single ovary contains but one ovule, and these at maturity 

 are completely coalesced, forming a caryopsis. 



Order Graminese. — The Grass Family. Herbaceous or rarely 

 woody plants, with round, jointed, and mostly hollow stems, bearing 

 alternate two-ranked leaves with split sheaths. (Figs. 334-9.) 



This very natural order contains about 4500 species, which are dis- 

 tributed in all climates. In the tropics they are large and almost tree- 

 like (Bamboo) ; in the temperate climates they cover the ground with 

 a close mat, while in the colder countries they grow in bunches. Very 

 many of the species are valuable on account of their starchy seeds or 

 nutritious herbage. None are poisonous (with possibly one or two ex- 

 ceptions). 



Tritlcum vulgare, Wheat, a native probably of Southwestern Asia, 

 has been under cultivation in temperate climates for several thousand 

 years. Remains of wheat grains have been found in the ruins of the 

 lake dwellings in Switzerland, proving that it was cultivated in Europe 

 in prehistoric times. By long culture it has formed many varieties ; 



