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 cespitosa (x about 30). 
Ridges 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 AHolcus lanatus, HMierochloe 
borealis 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 Hordez, whereas 90°/, of the Panicoidez and 
many species of all other groups have them. Examples 
of the sharply pointed form occur in Nardus, of blunt 
ones in Cynodon &c. 
In Nardus they occur on the leaf surface both 
Ww iy, 
