The Morphology of Ruppia Maritima. Ill 



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, I 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 corticalparenchyma(Pl. 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, u). 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 (PL 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. 



