616 Pearson . — On the Micro sporangium and Microspore of 
original structure save a shrunken, delicate, and interrupted outline (Fig. 7). 
The cells of the epidermis which now constitute the anther wall are some- 
what radially elongated, the outer wall being slightly thickened and cuti- 
nized. Running vertically from the summit of the anther for some distance 
down each side is a double row of cells smaller than the rest, and whose 
walls, at this stage, are less thickened. These are doubtless the rows 
described by Karsten between which dehiscence occurs. In all cases in 
G. africanuni they are smaller 1 than the rest of the cells of the w r all. 
The anthers, of which in all three species under investigation there are 
two on each flower-axis, are normally quite free from one another. Rarely, 
however, they cohere in the lower half. One case has been seen in which 
the septum separating them for more than two-thirds of their height was 
reduced to a cell-wall. 
In the stage of Fig. 5 the walls of the sporogenous cells are delicate, 
but in no way difficult to observe. Later, as the nuclei approach the 
condition known as synapsis, and while the tissue connexions are still 
maintained, the cell-walls become extremely thin and indistinct (Fig. 8). 
At this time the walls stain very faintly in Delafield’s haematoxylin or 
Lichtgriin ; but in unstained or badly stained preparations they are 
practically invisible. This must be the stage described by Karsten in 
G. Gnemon in which the sporogenous mass is said to consist of ‘ lediglich 
freie Zellen ohne Cellulosewande \ 2 During synapsis, when perhaps the 
wall is more difficult to distinguish than at any other time, the most careful 
observation of good preparations is necessary to convince one that Karsten’s 
description does not apply to G. africanuni . Here, however, there is no 
doubt that throughout this and the stages which immediately follow it, 
a wall is always present. After synapsis it undergoes a gradual thickening, 
but it does not become conspicuous until the condition of the ‘equatorial 
plate ’ is approached. The supply of material has not been sufficient for 
a detailed investigation of this remarkable behaviour of the wall of the 
mother-cell. There can, however, be no doubt that the substance of the 
wall on both sides of the middle lamella is actually removed, for the reti- 
culum of the cytoplasm can be seen to be in contact with the delicate 
separating membrane (Fig. 8). A similar series of changes has not been 
described for Ephedra nor for W elzvitschia. 
Soon after the distinct reappearance of the wall it undergoes a con- 
siderable degree of mucilaginous thickening, which, in early stages, is marked 
by the irregularity of its distribution (Fig. 9). At this stage many of the 
cells are partially separated from their neighbours (Fig. 9), though their 
isolation is not usually complete until after the conclusion of the heterotypic 
division (Fig. 10). When the mother-cells are quite free from one another 
the wall is thickened all round, but not uniformly so (Figs. 11-15). The 
1 Cf. Karsten (’93). 2 Karsten (’93), p. 345 . 
