326 Bower . — The comparative examination of the 
the centre of construction must lie relatively low : also that 
two conical cells are present, one on either side of the wall 
(x,x)\ their position relatively to it is however not exactly 
alike. I am disposed to regard those two cells which are 
marked (x,x) as the initial cells, notwithstanding their 
difference in form, and the fact that their size is not greater 
than that of the surrounding cells. It is interesting at the 
same time to note the grouping of the cells ; clearly the group 
to the right of the line (xf) has been derived from a conical 
cell, which has undergone a T division, while the upper left- 
hand cell thus derived has divided irregularly to form, among 
others, the obliquely-based initial (x ) : the group to the left 
of the line (x,x) was apparently derived from a cell with a 
square base, and after somewhat irregular divisions this has 
resulted in the formation of a conical initial cell ( x ). These 
remarks, which are not presumed to give any exhaustive 
account of the structure of the meristem as seen in longitudinal 
section, serve at least to indicate this : — that longitudinal 
sections bear out the conclusions drawn from the study of the 
meristem in plan, viz. that in strongly grown plants there is no 
single initial cell at the apex of the stem of the Marattiaceae, 
and that the series of segmentations of those cells which are 
believed to be the initials is far from being regular. 
I very much regret having to leave the investigation of the 
structure of these meristems in so unsatisfactory a position, 
neither being able to reduce the observations upon them to any 
strict system, nor being able to state directly that a definite 
system does not exist : such knowledge could only result from 
the examination of a very large number of specimens. But 
already my observations on the apex of the root of the 
Osmundaceae have shown that great irregularity and want of 
uniformity of construction are to be seen in them, and that 
irregularity which is found in the apex of the root of Osmun- 
daceae seems to find its parallel in the apex of the stem of the 
Marattiaceae. But though it is at present impossible to 
demonstrate a strict type of segmentation for the apices of 
the stems of these plants, the following general conclusions 
