On Pallavicinia decipiens, Mitten. 43 
is due to their being in reality wedge-shaped cells. It may 
here be pointed out that there is not a great dissimilarity 
between a wedge and a prismatic cell such as has been described 
for the growing parts of this plant A triangular prism may 
be conceived of as a broadened wedge, and the difference, so 
far as the plant is concerned, lies in the respective positions 
which such a wedge takes up in the apex. If its cleaving 
edge is directed inwards, and its head forms the free outer 
surface, then the ordinary 4 wedge-shaped ’ apical cell arises. 
If on the other hand, the wedge is situated so that its cleaving 
edge is directed vertically, its head ventrally, whilst its 
triangular sides form respectively the inner and outer faces of 
the cell, then a form of cell arises such as is met with in the 
growing axes of Pallavicinia decipiens. Moreover it is further 
possible that there is a special significance attaching to the 
shape of the apical cells occurring on these rudimentary 
adventitious branches, as pointing to an earlier type from 
which the triangular prisms of the rest of the shoots have 
been derived. 
Sexual Organs . — The plants, so far as my own specimens 
show, are strictly dioecious, and the antheridia and archegonia 
occur on the dorsal surface of the branches of the frond. 
The latter are grouped over a dichotomy, whilst the former 
occupy the length of one or more of the final branches of the 
frond, and are commonly situated on either side of the mid-rib 
in considerable numbers. A branch of the thallus bearing 
antheridia differs from the sterile ones inasmuch as it is con- 
siderably narrower, and in this feature it recalls the behaviour 
of the pinnae of many Ferns, where the sporophylls differ from 
the sterile leaves of the same plant (e. g. species of Lomarid). 
The antheridia arise as papilliform projections of cells very 
near the apex, and do not offer any special features of 
interest in their development. They ultimately form globose 
stalked bodies each situated in a depression of the frond, and 
roofed over by a scale which arises behind them, but leaves 
an opening anteriorly (PL VII, Fig. 18), through which the 
spermatozoids escape. 
