1 1 o Ford . — The A n atomy of 
trabeculae, which run across from the central cylinder to the 
outer peripheral layer. The root-apex is occupied by a well- 
marked apical cell (Fig. n) which is three-sided, the apex being 
covered by a root-cap of 2-3 layers. The apical cell cuts off 
segments in the three planes with great regularity ; vertical 
walls soon appear in these segments, then horizontal walls, and 
at a short distance below the apex the air-spaces are de- 
veloped. These arise as splits between the cells. Fig. 12 
represents a transverse section of a root just below the region 
of the apical cell, showing the regular arrangement of the 
cells and six developing air-spaces. 
Numerous lateral roots arise from the adventitious roots. 
These, according to Poirault 1 , are arranged in two rows ; each 
root arising from a single endodermal cell. Poirault also 
states that in Ceratopteris these rootlets do not always reach 
the exterior at once, for having made their way as far as one 
of the air-spaces of the mother-root, they grow for some time 
obliquely downwards before passing through the cortical 
parenchyma to the exterior. The material I have examined, 
however, did not show any of these internal rootlets. 
D. The Development of the Vascular System. 
The development of the vascular system in Ceratopteris 
thalictroides agrees, up to a certain point, with that found in 
many other Ferns. The later stages seem, however, to differ 
somewhat markedly from those described and figured in other 
cases by Leclerc du Sablon 2 . Figs. 2 to 8 represent the 
various stages met with in the development of the vascular 
system of Ceratopteris from the root upwards. Figs. 2 and 
3 are taken from the primary root of a young plant about 
a month old. Figs. 4-8 are from an older plant about three 
inches in height, in which the primary root had died away, 
numerous secondary roots having arisen to take its place. 
A little distance below the apex of the root the vascular 
tissue is differentiated. The xylem arises as two minute 
groups of tracheids (Fig. 2 } x) on each side of the bundle. 
1 Poirault, 1894, p. 121 . 2 Leclerc du Sablon, 1890, p. 5 . 
