ON GENERA AND SPECIES. 69 
instance, in C. arborea and C. serra, the fronds are terminal, 
forming the characteristic corona common to tree Ferns. 
When mature they separate from the stem, leaving a clean 
scar similar to Eremobrya, thus differing from the adherent 
vernation characteristic of the mass of the species of the 
tribe Cyathea; but as they agree in all the essential 
characters as regards the nature of their fronds and fructi- 
fication, it is therefore necessary to obtain more evidence 
as to the mode of evolution and structure of these tree 
Ferns before any satisfactory conclusion can be arrived at, 
as to enable us to view it as a special character to mark 
distinct genera.* 
This now leads me to notice another family of Ferns 
—namely, Marattiacee, which have a very distinct and 
special habit from other Ferns, and are well marked by the 
sporangia being destitute of a ring. The evolution of the ` 
arborea above noticed, but differs in the fronds rising 
from between two stipuliform appendages in the form of 
a socket, analogous to the stipules of pheenogamous plants. 
. The speciality of this group of Ferns leads me to view it ` 
as constituting a distinct division, which I have named 
` * Since the above was written, a valuable memoir * On the Structure ` 
and Formation of the Stems of the Tree Ferns of India,” has been — 
published in the thirtieth volume of the Transactions of the Linnean 
Society, 1874, by Mr. J. Scott, Curator of the Botanie Gardens, 
Calcutta. It consists of thirty-nine pages of lette=press, accompanied 
by eighteen plates. — poe pin Am jt iL 
frond is terminal and articulate to the caudex, as in Cyathea : S 
