278 MR. J. R. VAIZEY ON THE ANATOMY AND 
a stage a little later than that shown at fig. 32, division will have 
begun in the endomeristem, as shown by fig. 36, where walls are 
formed dividing the endomeristematic mother-cell of each quad- 
rant into two. The wall is in each case at right angles to either 
one of the octant- or quadrant-walls and parallel to the other 
quadrant- or octant-wall, as the case may be (fig. 36). A little 
later, in each of the cells thus formed another wall is formed at 
right angles to the one immediately preceding it and parallel to 
the one before that (fig. 37); each of these cells is again divided 
by walls again at right angles to the wall immediately preceding 
it and parallel to the one before that (fig. 38). This process 
then continues, so that the endomeristem consists of a number 
of cells which in transverse section have a rectangular 
outline. 
The law stated above for the divisions in the endomeristem 
holds good, I believe, so long as divisions go on in that tissue ; but 
beyond acertain point it becomes difficult to follow. Meanwhile, 
growth has been going on in the exomeristem, where divisions 
take place according to a different law to that obtaining in the 
endomeristem, in consequence of which the endomeristem is at 
once easily distinguished. In the exomeristem divisions take 
place in such a way that the cells are arranged in radial rows, 
and the radial walls are more numerous towards the periphery. 
After a time growth in the internal layers ceases, being carried 
on in the peripheral portions almost exclusively Ata very early 
stage the formation of tangential walls ceases absolutely in the 
innermost cells of the exomeristem. 
The best way of explaining the mode of development of the 
exomeristem is to follow the divisions of one of its peripheral 
cells and of the cells arising from that one. A comparison of such 
cells at different stages of their development will show that the 
cell is divided first radially by a tangential wall into two cells, 
one central, the other peripheral in position. The peripheral cell 
is then divided tangentially by a radial wall, and then each cell 
so formed is divided by a tangential wall, thus forming two radial 
rows. In the peripheral cells of each of the rows, either a tan- 
gential or a radial wall may be formed or a number of tangential 
walls; radial walls do not appear as frequently as tangential 
walls, and never two in succession. Divisions, both tangential 
and radial, appear in the peripheral, not in the central cells of & 
series. I think it extremely probable that, at any rate, radial 
