76 A. H. Graves, 
rounded so that intercellular spaces often occur, and elongated in the 
direction of the length of the stem (PI.I, fig. 5; Pl. III, fig. 7; Text-fig. 3). 
The majority of the cortical parenchyma cells show in an oblique 
view parallel horizontal stripes or bands on their side walls. A lon- 
gitudinal section proves that this appearance is due not to bands of 
thickening, but to slight undulations (Text-fig. 3). These are not 
necessarily regular in size or distance 
| | apart; they may or may not occur all 
through the cell, and certain cells are 
apparently entirely without them. Their 
function is not clear. Similar undulations 
were observed by Caspary (1858) in sev- 
eral aquatic plants, notably in Zannichellia 
palustris. Prillieux (1864) has also noted 
them in the stem of Althenia filiformis 
Figure 3.—Longitudinal nd in the roots of epiphytic orchids. 
section of a portion of Another point of general interest in the 
cortical parenchyma cells, stem cortex is the occurrence of starch 
showing undulations in 2 : 
the side walls. >< 210. grains. These, as ‘shown in Pl. I, fig. 5, 
are quite numerous. Their size evidently 
increases in the vicinity of the axial and cortical bundles and every- 
where at the nodes. Irmisch (1858, p. 35) has found starch abundant 
in the Potamogetons and has described its occurrence and appear- 
ance in considerable detail. 
In the cortex appear also the secretion cells noted in the epi- 
dermis, that is, they are apparently of the same nature, behaving 
in general in a similar way. They do not contain starch, as do 
most of the cortical cells, but are filled with fine granular contents 
and are especially abundant at the nodes. Bornet (1864, pp. 40-41) 
has noted cells evidently quite similar in the cortex and vascular 
tissue of Cymodocea, filled with a “liquide oléagineux, un peu teinte 
de jaune, tout-a-fait semblable a celui que renferment les cellules 
epidermiques des antheres.” 
In describing the cortex we may for convenience divide it into 
three portions: (a) an outer zone of cells, compactly arranged and 
bounded on the outside by the epidermis; (b) a central area, with 
a large portion of its territory occupied by a ring of lacunae or 
air spaces; and (c) an interior zone of cells limited on the inner 
side by the endodermis (PI. [, fig. 5). 
(a) Outer cortex. 
The outer portion of the cortex consists of two or three layers 
of cells (Pl. I, fig. 5 oc; Pl. Ill, fig. 7). The cells of the outermost 

