F ill c ales. 
i7 
fronds is very unlike, and Professor Bower’s view that the Schizaea- 
ceous annulus is a modified “ring” seems preferable to Potonie’s 
suggestion that it was originally a group of cells, in which case it 
might be compared to that of the Osmundaceae (31). 
The mesarch protostele of the oldest Osmundaceae recalls the 
structure of Gleichenia, but both protostely and mesarchy are not 
uncommon among the primitive ferns. The differences in their 
fronds and sporangia seem to show that though both are relatively 
primitive orders their common ancestor must lie a long way back. 
Though both Matonineae and Osmundaceae are true Ferns,, 
there can be little question of a close affinity between forms so 
unlike in their anatomy and soral characters. 
The Cyatheaceae, Polypodiaceae and Loxsomaceae are also 
clearly very remote from the Osmundaceae. The dictyostely of 
Osmundites skidegatensis certainly vividly recalls the stelar structure 
of many Cyatheaceae and Polypodiaceae, but it has been shown that 
it probably arose in a different way from the dictyostely of these 
two orders. The sporangia of the Osmundaceae also differ in mode 
of origin and in the structure of the annulus from the three other 
orders mentioned. 
Salviniace,e. 
The order of the Salviniaceae only contains the highly modified 
heterosporous and aquatic genera, Salvinia and Azolla. The 
obviously reduced stele consists of a small strand in which the 
first-formed elements are said to be central, though the xylem 
appears to develop somewhat irregularly (33). The leaves of Azolla 
are divided into dorsal aind ventral lobes. Those of Salvinia are 
arranged in whorls of three ; the dorsal leaf of each whorl is uni- 
fascicular and undivided, while the others are modified to serve as 
roots. The so-called sporocarp consists of a sorus completely 
enclosed in a coherent indusium. The megasporangium contains 
eight or sixteen spores. The gametophyte, especially the male 
prothallus, is much reduced. 
It is chiefly in their endarch protostely and the branching of 
their fronds in a dorsiventral plane that the Salviniaceae recall 
certain Botryopterideae. The writer, however, believes that the 
endarchy is in both cases secondary ; in the Salviniaceae it may be 
due to reduction of the stem. The different structure of the 
sporangia and the fact that the Botryopterideae disappear in the 
Permian, while the Salviniaceae are not certainly recorded before 
the Tertiary rocks, make it unlikely that there should be a direct 
connexion between the two orders. 
