336 Sutherland and Eastwood . — The Physiological 
with hairs, encircles the stem and prevents water or mud from lodging 
between it and the sheath. The long smooth pale-green sheath clasps the 
axis firmly, completely surrounding it for the greater part of its length and 
passing into the blade through the pulvinar articulation. The lower blades 
form angles of from 45 0 to 6 o° with the stem, while the upper ones are more 
erect. The angle increases with submersion. During the fall of the tide 
the leaves swing up and down in the surface film until they are suddenly 
released and spring into position. 
The adaxial surface of the blade is increased enormously by from 
forty to fifty ridges and furrows running from just above the pulvinus to the 
apex. These provide an increased assimilatory surface in addition to pro- 
tection for the stomata. The papillae and waxy coating on this surface 
give it a velvety and glaucous appearance. 
Root. The roots are adventitious and divided into two distinct sets. 
One type is long, relatively thick, smooth, and practically devoid of 
branches. This fixing form grows normally to a depth of six to twelve 
inches, serving to anchor the plant firmly in the soft mud. While its root- 
cap is large, root-hairs rarely, if ever, occur. The other type is shorter, 
thinner, and much branched, possessing a poorly developed root-cap and 
very sparse root-hairs on the youngest branches. Generally this latter form 
springs from, and clusters round the basal joints of the aerial axis, forming 
a densely woven, horizontal matting which aids largely in transforming the 
soft mud banks into comparatively firm turf. Similar tufts of branched 
roots spring from the rhizome nodes also. Their function is mainly absorp- 
tive. Both kinds of roots frequently show negative geotropism, probably an 
adaptation to the continuous silting. 
Anatomy. 
Epidermis. The adaptation of the plant to alternate aerial and 
aquatic existence is marked by peculiar and special epidermal structures 
wherein it differs from any other grass genus examined. The two most 
striking features are the very distinctive hydathodes and the forked accessory 
stomatal papillae, both of which are undescribed as far as we can ascertain. 
A distinct waxy coating covers all exposed portions above ground, 
giving the glaucous appearance. This is most pronounced on the adaxial 
surface of the leaves, where the epidermis is thinner, shows less cutinization, 
and is covered by numerous papillae as in Fig. 1, 1. These conical or peg- 
like projections also show little cutinization. On the narrow cells of 
the ridges they run along in pairs which frequently become coated over 
in the old fully developed leaves, as in Fig. 1, /, pd. This adds to the 
protection of the most exposed portions. The epidermal cells along the 
sides of the grooves are wider, and the number of papillae consequently 
greater. These, however, undergo no change. The papillae aid the waxy 
