12 Vert Brecuer Wrrrrock. 
cells are more seldom found in purely fertile specimens (pl. 2, fig. 1, 2, 
3). (On the different kinds of individuals as to the power of repro- 
duction, the fertile, the half-fertile-half-sterile, and the sterile, see below 
in this paragraph). At the time when the formation of spores is to 
take place, the formation of vegetative cells has ceased in purely fertile 
specimens, and the specimen has consequently attained its full size. 
All or most cells are then found to be so rich in chlorophyll, that the 
granules of chlorophyll form a continuous layer over the whole in- 
side of the cell-wall. The formation of spores is introduced by the 
upper part of the mother-cell of the spore (in P. kewensis nob. generally 
/,—'/, of the cell) widening a little (pl. 3, fig. 4s), so that it does at 
last assume the form of a rather slender cask; if the mother cell of the 
spore is a terminal cell, the upper end of the cask is pointed like a 
cone (pl. 3, fig. 5 s). It is this part of the cell that is to be developed 
to a spore. As yet, no change in the other part of the cell is percept- 
ible. But when the widening of the upper part is completed, the gra- 
nules of chlorophyll in the lower, cylindrical part of the cell commence 
to pass into the upper cask-shaped part. During this process it has 
seemed to me as if the parietal layer of chlorophyll were interrupted 
at the point where the cask-shaped widening of the cell commences — 
at least I have seen numerous cells during their formmg spores, in 
which the chlorophyllaceous body of the nascent spore has already 
at an early period been so sharply limited at the lower end, as pl. 3, 
fig. 6 shows. It is possible that, at this place, only a folding inwards, 
without a complete interruption of the layer of chlorophyll, has taken 
place. Be this as it may, at all events the parietal layer in the enlarged 
part of the mother cell of the spore does not suffer a displacement (for 
instance in such a manner that the chlorophyll in the lower part of the 
enlarged space were removed higher up), but, remaining in its original 
position, it 1s augmented in thickness by apposition from within, till 
the whole swollen part of the cell is filled with chlorophyll-coloured 
protoplasm. The chlorophyll from the lower, cylindrical part of the cell 
moves into the upper cask-shaped part (pl. 3, fig. 6), at the same time 
completely filling the space which has been occupied by the great central 
vacuole of the cell. This requires, as a rule, almost the whole chloro- 
phyllaceous mass of the cell, so that only a few granules of chlorophyll 
are left in the lower part (pl. 3, fig. 7). When the whole chlorophyllaceous 
mass has in this manner been completely removed into the upper and 
swollen part of the mother cell of the spore, the formation is commenced 
