78 MR. T. H. CORRY ON THE DEVELOPMENT 
of each of these long, narrow, prismatic cells becomes surrounded by an exceedingly 
thin and delicate but readily observable cellulose membrane, and forms an elongated 
club-shaped or fusiform pollen-grain, exhibiting therefore perhaps the most primitive 
type of pollen-formation known in the Phanerogams. In Aselepias, on the contrary, 
further division of each of the prismatic cells takes place, resulting ultimately in the 
formation of the special mother cells of the pollen in the following manner :— 
Succeeding the division of the nucleus of each of the prismatic cells into two parts 
(which feature, it has been already mentioned, was observable in some of the cells), the 
protoplasmic contents now divide vertically into two at right angles to the long axis of 
the cell, and therefore in the direction of the breadth of the anther, and at right angles 
to all the previous planes of division ; simultaneously the formation of a cell-wall takes 
place in the plane of division, 2. е. parallel to the short sides of the prism. By means of 
this septum the prismatic cell becomes divided into two smaller segments of oblong 
form and equal size *.` Тһе conspicuous nucleus of each of these oblong cells then 
becomes further subdivided by vertical division at right angles to the length of the cell. 
This division is followed by division of the protoplasm and formation of a cellulose 
septum running in the same plane. | 
The walls formed by the two last series of divisions are, of course, only visible in 
transverse sections. In the upper narrower part of the anther-lobe, the number of lon- 
gitudinal divisions which the primary mother cell undergoes is very small; and in conse- 
quence of this, fewer long narrow prismatic cells are visible in a transverse section 
through this part. Further, in this portion, sometimes only one of the two oblong cells 
formed by vertical division of the narrow prism divides again vertically ; so that in trans- 
verse section three cells only are apparent in an oblique row, viz. one larger and two 
slightly smaller. The cells formed by these successive vertical divisions of the narrow 
prisms, each with a conspicuous nucleus, are at first cubical; and in longitudinal section 
they are seen to be disposed in numerous more or less horizontal rows one above another. 
Soon, however, they become spherical in form (РІ. XVI. fig. 8), owing to the rounding- 
off of their walls on all sides, though they still remain firmly adherent together, and at 
the points where they touch adjoining cells there still exists only a common partition- 
wall They are the special mother cells of the pollen (sme, fig.8). At this period the 
mass of granular protoplasm contained in each of them cannot be discovered to have any 
special cellulose coat or wall deposited on it, but is surrounded only by the wall of the 
special mother cell. 
Thus none of the cell-walls so far produced in the whole course of the development of 
the pollen undergo absorption, as is commonly the case, and as Reichenbach has shown 
to take place in the waxy pollinia of the Orchids (where the mother cells are broken 
down, and form a viscid pulp in which the tetrads lie), but persist t—the cells which 
* The effect of all these divisions in the primary mother cells is merely to increase the number of mother cells 
from which the special mother cells are subsequently to be derived. 
+ Schleiden (Joc. cit.) states that the walls of the primary mother cells are absorbed in Asclepias, and that at a 
very early period. Such, however, is not the case. In Matas, according to Hofmeister, they are resolved together 
with those of the special mother cells. 
