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S. Reginald Price. 
markedly mucilaginous, and the mucilage is obviously formed by the 
swelling up of the cell-walls, with subsequent complete disintegration 
of the cells (Plate 6, fig. 1). This phenomenon is of course quite 
normal in root-caps, but probably here the mucilage formation is 
rather exaggerated. 1 
Coming to the root-tip itself, the most striking feature is the 
character of the cells which compose the outer layer of the cortex— 
the piliferous layer. This layer is composed of regularly arranged 
cells, each cell being slightly elongated in a direction perpendicular 
to the root-surface (Plate 6, figs. 1 and 2). The anticlinal walls 
are straight and parallel, while the outer tangential walls are 
rounded or sometimes slightly conical. This rounding of the free 
wall is evident quite close to the apical meristem. The whole outer 
layer appears as a regular palisade of cells on the outside of the 
root. Each of these cells seems to act as a mucilage-secreting 
gland, the outside of the root being covered by a wide layer of 
mucilage resulting from the activity of these glands. The cells 
appear to function thus almost as soon as they are formed, for a 
thin layer of mucilage extends almost up to the apical cells, between 
the tissues of the root-cap and root-tip, this layer gradually be¬ 
coming thicker as we pass away from the apex (Plate 6, Fig. 1). 
The mucilage appears to be actually secreted gradually by the 
cells, and is not formed by the wholesale conversion into mucilage of 
the outer walls. In some cases the mucilage layer was torn off in 
cutting (Fig. 4), or removed by hydrofluoric acid, but the glandular 
cells still retained their contour and showed a perfectly distinct 
outer wall. It is also noticeable that the mucilage secreted by these 
cells stains rather more deeply with Diamant Fuchsin than does the 
mucilage formed by the root-cap cells. The wide layer of mucilage 
exhibits slightly marked radial striae which correspond to the 
divisions between the secreting cells. There is also a series of 
tangential striations which are arranged roughly concentrically with 
the tangential outer walls of the cells (Figs. 3 and 4). This system 
of striations may indicate that mucilage formation takes place by 
the modification and swelling of the outer portions of the cell-walls, 
which are constantly renewed by the protoplasm within the cells— 
quite a different process from the simple swelling of a wall to become 
mucilaginous, in that it is continuous and progressive. The activity 
of these cells is also indicated by their very dense protoplasmic 
Van Tieghem, l.c., Fig. 458, and also Strasburger, Text-boob of 
Botany, Eng. Trans., 3rd Edn., London, 1908, Fig. 168. 
1 
