Iv] VASCULAR BUNDLES 67 
Bristles—i.e. long, sharp, stiff hairs—are not very 
common. They occur on Nardus, Anthoxanthum Puelii, 
Panicum, Cynodon. 
Papillz occur on the leaves of Glyceria, Nardus, 
Leersia, &e. 
Poa pratensis has soft hairs on the upper epidermis. 
The stomata of Sesleria cerulea are depressed and 
six-celled, two guard-cells being overgrown by four ac- 
cessory cells, but in most grasses they are of the ordinary 
type with two elongated guard-cells only. 
As regards the vascular bundles constituting the 
venation, they are as is well known parallel from base 
to apex in our common grasses, with linear leaves, and 
Fig. 25. Transverse section of part of leaf of Elymus arenarius, partly 
inrolled (x about 30), showing ridges of unequal height, of which 
the higher are flat above. Vascular bundles girdered, the stronger 
above and below. Motor-cells in each groove cause the inrolling of 
the lamina by their contraction. 
are usually of four orders as regards strength. Those of 
the first (e.g. mid-rib) and second orders have conspicuous 
vessels, but those of the third and fourth orders may be 
practically devoid of vessels, though xylem and phloem 
5—2 
