APEX OF THE ROOT IN OSMUNDA AND TODEA. 
81 
meristem found in Osmunda regalis, that which is perhaps 
the most interesting from a theoretical point of view, is that 
represented with varying clearness in the figs. 6, 7, and 8. 
In each of these figures it may be seen that the whole tissue 
is referable in its origin to three initial cells, which are marked 
(x), while the three walls separating these cells from one 
another meet at a central point. These three walls are drawn 
in heavier lines, and may be traced for some distance from the 
central point; they may be called the principal walls (p in 
the figures, Cf. Hauptwande, Naegeli andLeitgeb). In each 
case the portion of tissue derived from one of these initial cells 
is enclosed between two of these principal walls, and thus the 
whole meristem may be regarded as consisting of three wedge- 
shaped masses. Taking now those masses singly into consi- 
deration, it will be clearly seen that in fig. 6 each is divided 
into two unequal parts by walls marked (s), which do not 
proceed to the centre, but on passing towards it curve 
gradually out of the radial plane, and insert themselves at 
right angles on the principal walls : these may be called the 
sextant-walls (Cf. Sextandenwande, Naegeli and Leitgeb.) 
A similar arrangement, but less clearly marked, may be seen 
in such examples as those represented in figs. 7 and 8. In each 
case the error of regarding sections below the real initial cell 
or cells as including the initial cells, has been carefully 
avoided ; that the fig. 8 actually represents the apical group, 
and not apart of the tissue below it, is proved by the fact that 
the section includes division walls characteristic of the root 
cap, one of which is represented by the dotted line ; this comes 
into view only on focussing deeply into the section : the cell 
walls drawn in this figure as continuous lines are those seen on 
observing the section from the side more remote from the 
root cap. 
For comparison with this arrangement of the initial cells and 
their derivatives I have quoted, as figs. 9 and 10, two of the 
drawings of Naegeli and Leitgeb, which appeared in their well- 
known work, ‘ Entstehung und Wachsthum der Wurzeln, 5 as 
Taf. xii, fig. 8, and Taf. xiv, fig. 5. These represent optical 
VOL. XXV. NEW SER. 
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