34 ° Sutherland and Eastwood . — The Physiological 
three, close rows on each side of the laminar furrows. These rows (Fig. 4,2) 
are about two cell-widths apart, and almost corresponding distances from 
the motor-cells forming the bottom of the groove, and the line of hyda- 
thodes nearer the angle of the ridge. The stomata are of exceptional 
interest on account of the unique structure and placing of the papillae on 
the subsidiary cells. The papillose epidermis of this surface has been 
noted already. There are two massive papillae on each subsidiary cell, 
placed opposite the end of the stomatal slit (Fig. 2, 1 and j). These ex- 
pand at the top into two, three, or more rarely four, short branches which 
are strongly lignified, like the thickened walls of the guard cells. Fre- 
quently there is a simple papilla between them, corresponding to the 
middle of the pore. All bend over the guard cells, forming a fringe round 
and over the stoma as in Fig. 2, 1. 
A small piece of leaf immersed in water showed a tiny air-bubble 
captured by these furcate papillae. Doubtless when the leaves are sub- 
merged the entangled air-bubbles prevent the entrance of water through 
the slits, and in this way the most active stomata are prevented from 
admitting water into the air-spaces at a time when they are open or 
partly so. This apparatus, along with the simple papillae and the waxy 
coating, goes a long way towards an explanation of the plant’s adaptation 
for its dual existence. 
The normal type of storim occurs sparsely over all chlorenchyma. 
They are abundant on the inner epiderm of the sheath, but then it presses 
so tightly against the stem that no water gains entrance. Although their 
appearance on the rhizome sheaths is more surprising, the absence of chlo- 
rophyll prevents the manufacture of osmotic substances, and consequently 
the guard cells are inert. 
Hydathodes. Hydathodes of a type apparently hitherto undescribed 
take the place of the water pores found in many submerged plants, being 
distributed widely in definite tracts in the active chlorenchyma, usually 
near large water-storing cells. On the upper surface of the leaf they are 
arranged in a row (Figs. 1 and 4) along each side of the furrow, about two 
or three cell-widths from the ridge angle, and one or two from the upper 
line of stomata. Here the epiderm consists of long cells alone, and the 
hydathodes are placed between every two or three of these in longitudinal 
series. On the abaxial surface of the leaf-blade and sheath they form 
a similar line in the large-celled tissue between the sclerenehyma bands 
over the bundles. They are absent from the rhizome, the invested portion 
of the stem, and the inner surface of the sheath, but occur abundantly 
on peduncles, and even glumes in the more-pronounced assimilatory bands, 
although always near fairly large cells with watery content. They are 
placed invariably between the ends of two long cells which become slightly 
narrower as they approach one another (Fig. 3, /). However, instead 
