IV 



GIRDERS 



69 



annua (Fig. 21), P. bulbosa, P. conipressa and Dactylis 

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

 (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 stricta ( 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 sclerenchyma, 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, Gynodon — or 

 above and below each of the other bundles as well — 

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

 cwspitosa (Fig. 23), Holcus lanatus, Glyceria aqnatica, 

 G. Jiuitans, Digraphis, Elynius (Fig. 25), Agrupyrum 



