meristems of Ferns as a Phylogenetic Study. 313 
walls present a distinctly convex internal surface : thus while 
in this root a cell is present which may be recognised as a 
pyramidal apical cell, the whole construction approaches that 
of the co-axial or fan-like type. 
Lastly, the less common, but very interesting arrangement 
shown in Figs. 8 and 9 must be mentioned. Here no pyra- 
midal cell is to be found ; the median longitudinal section 
shows two cells (x, x) of truncated pyramidal form, from 
which segments are cut off, (1) from the base, to form tissues 
of the root-cap ; (2) from the sides, and (3) as shown in Fig. 8, 
from the truncated apex also. In this case the correspond- 
ence with Schwendener’s description 1 of the apical group in 
the root of the Marattiaceae is very apparent. 
It has been demonstrated repeatedly by various authors 
that in the cases of Equisetum and many Ferns there is a cer- 
tain order of succession and regularity of position of those 
walls by which the segments are divided up into smaller cells. 
A comparison of the drawings above quoted, with those of 
Naegeli and Leitgeb, will suffice to show that in Osmunda the 
outer limit of the procambial cylinder does not appear to cor- 
respond to any definitely recurring wall in the young seg- 
ments, as is the case in the roots investigated by Naegeli. 
The same may be said with respect to the limits of the cortex 
and epidermis ; the latter tissue, which can readily be recog- 
nised in the older part of the root, and can be traced as 
entering below the layers of the root-cap, loses its identity at 
a considerable distance from the actual organic apex of the 
meristem. This fact is illustrated in the Figs. 6 and 9 : in 
neither of these examples can a clear distinction be drawn 
between those cells which will develop as tissue of the root- 
cap and those which will form epidermis or cortex. 
The results now detailed have been further supported by 
observations on young developing lateral roots: in Fig. 10 is 
shown a young lateral root in median section, and here are 
seen two oblong initial cells which accord in form and position 
to those shown in Fig. 8, while the case of Fig. 11 shows a 
1 Sitz. d. K. Preuss. Akad. d. Wiss. 1882. 
