IV] 



GIRDERS 



69 



annua (Fig. 21), P. bullosa, P compressa and Dactylis 

 glomerata. In Festuca ovina, F. rubra, F. heterophylla 

 (Figs. 18, 27) there are groups more or less pronounced at 

 the keel and margins, or even a continuous band below, 

 but none above the bundles. 



Fig. 26. Transverse section of leaf 

 of Nardus striata ( x about 50). 

 The upper surface is repre- 

 sented by the four grooves and 

 five ridges, each of the former 

 with traces of motor-cells at its 

 base. The deep shaded por- 

 tions are sclereuchyma, strong 

 girders of which join the vas- 

 cular bundle of each ridge to 

 the lower surface. This type 

 is obviously derived from that 

 in Fig. 19, and may be regarded 

 as a permanently rolled leaf. 



Fig. 27. Transverse section of 

 leaf of Festuca ovina, var. 

 duriuscula ( x about 50), the 

 type of a permanently folded 

 leaf. Seven ridges and six 

 intervening grooves are seen : 

 each of the latter with traces 

 of motor-cells below. In each 

 ridge is an isolated vascular 

 bundle, and a narrow scleren- 

 chyma baud below. 



Many grasses have an isolated band above and below 

 each primary bundle only — e.g. Panicum, Cynodon — or 

 above and below each of the other bundles as well — 

 e.g. Spartina, Arundo, Polypogon, Agrostis alba, Aira 

 ccBspitosa (Fig. 23), Holcus lanatus, Glyceria aquatica, 

 G. fluitans, Digraphis, Elymus (Fig. 25), Agropyrwni 



