№ 
76 MR. Т. Н. СОККҮ ON THE DEVELOPMENT 
divisions successively occur. The cell which constitutes the innermost of these three 
layers forms by radial division a peculiar epithelium of rectangular cells, investing on 
the inside the primary mother cell : this is the tapetum (Pl. XVI. figs. 2,3, & 4, tap). The 
cells of the tapetum proper are reinforced by a corresponding layer on the external side 
of the anther-lobe, formed by means of a series of internal segments, cut off vertically 
from the cells of the parenchymatous ground tissue in that region (Pl. XVI. figs. 3-9, 
tap*). In this manner a limiting membrane is formed, which entirely surrounds and 
invests on all sides the primary mother cell of the pollen. 
The tapetal cells proper are thus derived from a portion of the primitive archesporium, 
while those cells by which the layer is completed towards the outer side of the anther, 
and which appear in transverse section to be longer and more oblong than the real 
tapetal cells, are not so derived. Each cell of the limiting membrane contains a pro- 
minent nucleus surrounded by granular protoplasm. | 
The primary mother cell of the pollen is, when viewed in transverse section, at first 
somewhat hexagonal in shape, single, and of relatively large size; for while the outer 
segment of the archesporial cell has continued to undergo division, no further division has 
taken place in the inner segment, which possesses very granular protoplasmic contents 
anda distinct nucleus (Pl. XVI. fig. 6, mc). Very soon, however, it may be found exhibit- 
ing two nuclei produced by the division of the single one; and this nuclear division is 
speedily followed by a division of the protoplasm into two portions, and formation of a 
longitudinal septum in a direction somewhat oblique to the surface of the anther. Each 
of these two cells now begins distinctly to elongate in a direction perpendicular to the 
surface of the anther; and by virtue of this elongation they become very sharply dif- 
ferentiated from the surrounding tissue. As the loculus expands by growth of its walls, 
this elongation becomes more and more pronounced. Immediately after this change has 
become fairly well marked, each of the two cells becomes divided by longitudinal divi- 
sion parallel to its longer axis; and this is followed by a transverse, $.е. horizontal 
division, also parallel to its longer axis, and therefore at right angles to the last. 
The cells, in consequence of this, take the form of short prisms, whose direction is 
inclined obliquely downwards from the surface (Pl. XVI. fig.7). Of these prisms four 
appear in transverse section; and the free faces of the two lateral ones are somewhat 
rounded, so that the whole mass has now a slightly elliptic form. Further division 
of each of these prisms is then continued in both the longitudinal and horizontal planes 
parallel to the longer axis of the cell; the result of which is that the loculus of the 
anther now contains a large group of cells, comparatively narrow in proportion to 
their length, which appear in any transverse section as a single row, consisting of from 
eight to twelve or more cells. Seen in this view they are of extreme length, being six 
to ten times longer than they are broad, of large size, and rhomboidal or prismatic form, 
while they pursue a slightly oblique direction. Each possesses very granular protoplasmic 
contents, containing a large circular nucleus with a nucleolus, a large vacuole at each 
end, and а thin cellulose cell-wall. Their vertical or longitudinal walls form а common 
partition between these cells, on the one hand, and the cells of the tapetal limiting mem- 
brane, which closely surrounds them, on the other. Some of them may, at a slightly 
ж. 
