V] LEAF-STKUCTURE 76 



P. prateiisis 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 distrihuted 

 between the ridges. 



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 uith girders above and 



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 PJuxig mites. 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 d fficult 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 mas.s below, and 

 larger lacuncc. 



