238 Campbell. — On the development 
others more recently investigated, the episporium is derived 
from the epiplasma, and must therefore be regarded as an 
entirely independent membrane and not as a part of the 
exosporium. 
The spore (PL XIII, Fig. 1) contains an easily-demonstrable 
nucleus, and is filled with densely granular protoplasm in 
which, as we have already seen, are imbedded numerous starch- 
granules. - 
The first wall formed in the germinating microspore (PI. XIII, 
Fig. 2) is at right angles to the shorter axis of the spore, and 
divides it into a small basal cell and a much larger upper one, 
the mother-cell of the antheridium. The basal cell frequently 
becomes further divided into two cells of very unequal size, 
which represent the vegetative part of the prothallium. In 
the mother-cell of the antheridium there is next formed a wall 
which corresponds to that formed in the mother-cell of the 
antheridium of the Polypodiaceae. It is more or less dis- 
tinctly concave above, and may be funnel-shaped, meeting the 
basal wall (PI. XIII, Figs. 3, 4 m). This wall is followed by 
a dome-shaped wall whose base is in contact with it, but 
the upper part usually free and approximately concentric with 
the outer wall of the spore (PL XIII, Figs. 3, 4 n), but not in- 
frequently cases were observed where it was to a greater or less 
extent in contact with the endosporium, so that the cell thus 
formed has its wall in part made up of the endosporium (PL XIII, 
Fig. 5). This cell is the central cell of the antheridium, and 
from it alone are derived the mother-cells of the spermatozoids. 
Finally a ring-shaped wall is formed at the top, constituting 
the cap-cell of the antheridium. The succession of walls in 
the mother-cell of the antheridium, as will be seen from the above 
statement, follows almost exactly that of the Polypodiaceae, and 
shows a much less reduced state of the antheridium than was 
supposed to be the case ; indeed occasionally the vegetative 
part of the male prothallium of certain Polypodiaceae (e.g. 
Asplenium Filix-foemina) may be reduced to a single cell 1 , and 
1 D. H. Campbell, The Prothallium of Ferns, in Botanical Gazette, 1885. 
