593 
Ford. — The Anatomy of P silo turn triquetrum. 
parenchymatous region (Fig. i, p' ci) immediately surrounding the stele. 
The cell-walls of this tissue are perforated by numerous oval or circular pits, 
which vary in size. Starch is generally found in the cells, and in the lower 
and older parts of the plant conspicuous nodules of varying shape and size 
(Fig. i, n) are also present. These nodules are unaffected by acetic 
and nitric acids, and the fact that they are left as an insoluble residue after 
several days’ maceration and boiling in Schulze’s macerating fluid suggests 
the presence of silica. 
The endodermis, which Bertrand describes as a badly defined layer, is 
however clearly recognizable, after suitable treatment or after staining, when 
the thickenings on the radial walls stand out very distinctly (Fig. 2). 
The centre of the stele is occupied by a group of sclerenchymatous 
fibres (Fig. if ) ; the walls of these have numerous, small, simple pits. In 
the stouter parts of the plant the fibres form a conspicuous group ; higher 
up the number gradually decreases until only two or three, and finally none 
at all, are present. The xylem surrounds the central group of fibres with 
a star-like outline, the projecting points marking the position of the 
protoxylem-groups, the number of which varies with the size and region of 
the stem. In stouter branches nine or ten may be found, in the small apical 
branches two or three only may be present. In the latter case the xylem 
may be present as a small central strand, or it may form two small masses 
lying close together, each containing one group of protoxylem. The xylem 
is made up of ordinary scalariform tracheids, the protoxylem of spiral 
elements. 
Between the endodermis and the xylem a mass of tissue is found which 
is very difficult to differentiate. Seen in transverse section, there is no 
clearly defined pericycle, the tissue consisting of a mass of parenchymatous 
elements of varying size. Treatment with aniline chloride gives signs of 
lignification 1 in some of the cells, especially at the corners ; and this is more 
noticeable in the tissue lying outside the projecting tips of protoxylem 
(Fig. 2). In longitudinal sections the main mass of the tissue is seen to be 
composed of elongated parenchymatous cells (Fig. 4 , pa) with conspicuous 
nuclei. Staining with chlor-zinc-iodide shows that the walls of these cells 
are covered with numerous small oval or circular pits or pores. Besides the 
nucleated parenchyma, long tube-like elements (Fig. 4, st) occur singly, or 
occasionally one or two together, which may possibly be regarded as sieve- 
tubes. These tube-like elements are frequently crowded with granules 
which stain yellow with chlor-zinc-iodide. With Delafield’s haematoxylin 
the walls stain a deeper blue than in the case of the ordinary parenchymatous 
cells, and scattered globular masses are found of varying size (Fig. 4, m) 
which stain very deeply. These are probably of the same nature as the 
1 Vaughan Jennings and Hall state that in Tmesipteris they failed to find lignification of the 
phloem, but the material at my disposal showed it far more noticeably and clearly than in Psilotwn. 
