V] LEAF-STRUCTUEE 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. annna agrees in the latter point. 



** Leaf not keeled : rollvng wp. Motor-veils distributed 

 between the ridges. 



+ 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 lacunae. 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 Donax is very like A. Phragmites, but has larger bundles 

 each with a horse-shoe shaped sclerenchymatous mass below, and 

 larger laounse. 



