The Morphology of Ruppia Maritima. 111 
persist in this way—becoming broken off. Their ‘basal parts then 
appear as blackened dead cells in the epidermis. 
Leavitt (1904, p. 279) lays considerable stress on the small size 
in general of the trichoblasts and bases of trichomes as compared 
with the ordinary epidermal cells. In Ruppia, while some of the 
trichoblasts and bases of mature trichomes may occasionally be 
somewhat shorter, on the whole they average about the same size 
as the non-piliferous cells, even from the very first appearance of 
the trichoblasts (Pl. VI, figs. 29, 32, 33). In her paper on root 
hairs, Miss Snow (1905), from the study of several species, assigns 
no definite length to the hair-producing cells, but announces that 
in the same root the average length of the trichome-cells is less 
than that of the atrichomic cells. 
b. Cortex. 
Although to the cortex proper belong genetically the exodermis 
described above under the head of epidermal tissue, the cortical 
parenchyma, and the endodermis, | am describing each separately. 
Varying with the thickness of the root, from six to twelve concentric 
rings of large, rounded, thin-walled cells with diamond-shaped, schizo- 
genous intercellular spaces, form the cortical parenchyma (PI. VI, fig. 27). 
Often, in the mature root, on account of the radial expansion of the 
tissues, these parenchyma cells undergo a stretching, and separate 
from each other laterally, producing long strings of collapsed cells. 
A longitudinal section proves that the intercellular spaces of the 
cortical parenchyma in the region of the endodermis, are often of 
a somewhat peculiar nature (Pl. VIII, fig. 47, w). These spaces 
arise by a local splitting of the wall, the split parts curving outward 
in opposite directions, forming openings which in the longitudinal 
section appear from spindle-shaped to circular in outline. These 
spaces may occur in series or singly at intervals. Near the 
endodermis they are small, increasing in size in the direction of 
the middle cortex. Before we come to the middle cortex, however, 
we find them elongated into long narrow canals, of which the 
diamond-shaped spaces described above are cross-sections. 
c. Endodermis. 
A single—occasionally, in places, double—ring of cells surrounding 
the vascular bundle, comprises the endodermis (PI. VIII, fig. 46). 
Its radial walls show to a very slight degree the typical endodermal 
thickenings. The tangential walls are minutely wavy at irregular 
intervals. After treatment of cross-sections of the root with con- 
centrated sulphuric acid, the endodermis as well as the epidermis 
and exodermis remain clearly defined. 
