IV] EPIDERMIS 65 



at right-angles, and some epidermal and parenchyma 

 cells — especially below the stomata — have solid masses 

 of silica filling the lumina. 



Fig. 23. Part of transverse section of leaf of Aira cmspitosa ( x about 30). 

 Eidges very high and acute, each tipped with sclerenchyma, and 

 containing an isolated vascular bundle — sometimes one or more 

 small ones also. Motor-cells well developed at the base of each 

 groove. The bundles are not girdered, but numerous bands of 

 sclerenchyma almost join into a continuous band below. The 

 leaf rolls inwards. 



Short cells occur in Holcus lanatus, Hierochloe 

 horealis and Dactylis glomerata interspersed between 

 plane-walled cells. They may be silicified and vary in 

 shape — square, saddle-shaped, elliptical, irregular, &c. ; or 

 they may be replaced here and there by asperities — e.g. 

 Elymus — or in rarer cases by stomata. Grob has at- 

 tempted the classification of their distribution in different 

 grasses, but the subject is too complex for treatment here. 



The epidermis of many grasses is studded with short 

 two-celled hairs bent sharply at right-angles ; so that 

 the pointed or blunt, hollow or solid, apical portion is 

 appressed to the surface. Grob says that these are absent 

 from the Hordeae, whereas 90 % of the Panicoidese and 

 many species of all other groups have them. Examples 

 of the sharply pointed form occur in Nardus, of blunt 

 ones in Qynodon &c. 



In Nardus they occur on the leaf surface both 

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