meris terns of Ferns as a Phylogenetic Study. 365 
subsequent divisions to form the tapetum may be inclined to 
one another, so that the sporogenous cell is ultimately tetra- 
hedral, as in Osmunda (Fig. 77). In its further development 
the sporangium of Todea corresponds closely to that of 
Osmunda (compare the diagrammatic Figs. 88, d , e.). 
Observations have also been made on the filmy Todeas (T. 
superba , and T. hymenophylloides ) : in both of these the spo- 
rangia are seated only on the more massive nerves, and do not 
arise from the filmy part of the pinnules. In these species 
the first stages of development were not noted, but sporangia 
were seen corresponding closely in structure to those of 
Osmunda (Fig. 77), and all observations I have made point to 
the conclusion that the development of the sporangium is in 
these species essentially similar to that in Todea barbara , or 
Osmunda regalis. 
The mode of origin of the sporangium in the Marattiaceae 
is well known through the researches of various writers, but 
especially of Goebel 1 : for our present purpose the most 
notable points with regard to it are (1) that the sporan- 
gium is not directly referable in its origin to a single cell, i. e. 
it is eusporangiate ; (2) that the archesporium is the hypoder- 
mal cell of the axile row of those cells which grow out to form 
the sporangium ; (3) that it has a cubical form, and is deeply 
sunk in the tissue of the sporangium ; (4) that the tapetum is 
derived from the cells surrounding the archesporium ; (5) that 
the wall of the mature sporangium consists of more than a 
single layer of cells ; and (6) that the sporangia which indi- 
vidually produce a relatively large number of spores, are 
massed together into bulky confluent sori (compare Figs. 
88 ,/,*). 
From a comparison of the characters of the young sporan- 
gia above noted, and of the diagrammatic figures (Figs. 88, a-g) 
which embody them, the following conclusions may be drawn : — 
(1) That as regards the complication of the mode of origin, 
and the complexity of structure of their sporangia, the Hy- 
menophyllaceae and Polypodiaceae, the Schizaeaceae, Osmun- 
1 Bot. Zeit, 1881, p. 681, etc. 
