I 20 
Daisy G. Scott. 
of origin of the tissues of all roots, whether of Dicotyledon or of 
Monocotyledon, is the same, each root having three sets of initials 
which give rise respectively to (1) the plerome, (2) the cortex, 
(3) the epidermis ( = root-cap). He holds that the epidermis is 
many layered at the apex and that the external layers act as a 
root-cap, while the outermost central cells furnish the piliferous 
layer. 
In the following notes an attempt is made to determine the 
mode of origin of the different embryogenic layers in the roots of 
the following genera of Monocotyledons, viz.:— Alisma, Butomus, 
Vallisneria, Ruppia, Zostera, Naias, Strntiotes, and Limnocharis. 
I propose, first of all, to describe my own observations, with the 
help of the figures, and afterwards to attempt certain general com¬ 
parisons of the results obtained from those observations. 
The materials used were the stems of representatives of the 
genera named shewing the points of origin of lateral roots. The 
material was stained, embedded, and cut in the microtome by the 
paraffin method in the usual way. 
Alisma. Plate IX. Figs. 1 to 4. 
A young root is shewn in longitudinal section in Fig. 1. The 
plerome cylinder is distinct, and has a single initial. Tho 
periblem and dermatogen form a single layer at the apex. The 
calyptrogen is at this stage only one cell in thickness. 
An older stage is represented in Fig. 2. The plerome cylinder 
is now distinct, and is terminated by a single initial cell. The 
axial row of cells seen so clearly in most roots examined is not 
so distinct in Alisma as in many of the other genera. In transverse 
section of a root (Fig. 3) at much the same stage of growth as Fig. 
2, a cell of the axial row is seen with one layer of plerome cells 
grouped round it, surrounded in turn by periblemic tissue. Re¬ 
turning to Fig. 2, the dermatogen has been split off from the 
periblem and is shewn as a single layer; both dermatogen and 
periblem, have, however, a common origin in the single initial cell. 
The cells of the cortex to the exterior show a width greater than 
those more internally placed. This is also seen in Fig. 3, which 
shews that since the same approximate number of cells are present 
in each concentric layer of the cortex, the cells in the external 
layers must widen in a tangential direction. The calyptogen at the 
stage seen in Fig. 2, is four layered. 
No longitudinal section was found shewing the embryogenic 
tissue fully differentiated into tissue elements. A transverse 
