478 



PART IV. CLASSIFICATION*. 



of the seed. In other Monocotyledons either the cotyledon is a 

 sheathing scale, or it is the first green leaf differing but little 

 from the foliage-leaves which are subsequently developed. 



The primary root usually remains small and inconspicuous : in 

 Grasses generally, the radicle begins to branch before it escapes 

 through the micropyle on germination, so that the root is then 

 fibrous ; when this is the case the inadequate root-system is sup- 



FIB. 292. Grain of Triticum vulgnre, the V/heat. A Cross-section thronghthe pericarp 

 and testa. Of tbese, ep is the epidermis, e the enter layers, and cM the chlorophyll. 

 layer, of the pericarp : ti remnants of the ovular integument, and n the outermost 

 thickened layer of the nucellus; these together constitute the testa: ol the alenron- 

 layer of the endosperm (x 210). JB Median longitudinal section through the lower 

 part of a ripe grain, in the plane of the furrow. At the bottom of this to the left ia 

 the embryo: the scutellum, ic ; I' the ligule of the scutellum ; rs its vascular bundle; ce 

 its layer of cylindrical epithelium: c the sheath of the plumule (coleoptile); pv the grow- 

 ing-point of the stem; hj> the hypocotyl ; I thecpiblast; r the radicle; cp the root-cap of 

 the radicle ; el the root-sheath (coleorhiza) ; m phice of exit of the radicle, corresponding 

 with the micropyle of the ovule ; p the funicle ; vp vascular bundle in the funisle : / 

 lateral surface of the furrow (x 11). (After Strasburger.) 



plemented by the development of adventitious roots in succession 

 at higher and higher levels upon the stem. 



The stem of Monocotyledons is traversed longitudinally (Fig. 

 99, p. 122) by scattered closed vascular bundles (Fig. 103) , it has 

 therefore no growth in thickness by the means of cambium. In 

 a few genera only, as Yucca and Dracaena, it grows subsequently 



