v] LEAF-STRUCTURE 75 
P. pratensis are devoid of the hooked asperities; P. nemoralis has a 
thicker lamina than the rest, and girders to the secondary bundles. 
P. annua agrees in the latter point. 
** Leaf not keeled: rolling up. Motor-cells distributed 
between the ridges. j 
t Hairs none or rare, or at most a few asperities. 
= Veins numerous, 30—40 on each half lamina. 
Motor-cells very large. 
© All vascular bundles with girders above and 
below. 
Digraphis arundinacea. No keel. Marginal scleren- 
chyma conspicuous. <A few asperities below. Leaf thin, 
and all the bundles joined to the epidermis above and 
below by girders (Fig. 14). Stomata on both surfaces, 
fairly large: epidermal cells with plane walls. There may 
be a few irregular air cavities, especially near the mid-rib. 
©© Only the principal bundles girdered. 
Arundo Phragmites. Ridges very numerous and low. 
No keel. Marginal sclerenchyma strong. Vascular bundles 
with sheaths of large colourless cells, a few of the strongest 
girdered below, but most have only sclerenchyma bands 
above and below. Motor-cells particularly large, between 
all the bundles. There are no conspicuous lacune. Hairs 
very rare. Epidermal cells small, with sinuous walls: all 
the cell-walls contain silica. Stomata on both faces, sunk, 
small and more difficult to see than in Digraphis, where 
the epidermal cells are plane walled, or nearly so. 
Arundo Dona is very like A. Phragmites, but has larger bundles 
each with a horse-shoe shaped sclerenchymatous mass below, and 
larger lacunee. 
