42 ON GENERA AND SPECIES. 
side. This, according to my view, accounts for the ring .- 
appearing not to be iruly vertical, but it is to be observed 
that the obliquity is not general, for in the figures of the 
Sporangia of eight Cyatheaceous genera in Hooker and 
Bauer's “Genera Filicum,” the ring is shown. to be verti- , 
cal I therefore follow Robert Brown in placing Oyathee 
in Polypodiacee. 
The next systematic work to be noticed is that of 
Professor Mettenius, of Leipzig, who, in 1858, commenced 
publishing a work entitled “ Uber einige Farngattingen ” 
(“On Some Genera of Ferns ”), of which five parts have 
appeared. In order to explain this author's system of 
classification of species, I will give a brief outline of the 
manner in which he treats the genus Polypodium, He 
enumerates, and mostly describes in full, 258 species of 
this genus, including in it all the forms possessing puncti- ` 
form, oval, or linear, naked sori, thus restoring it to nearly 
the state in which it was left by Swartz, Willdenow, and 
Sprengel, and even including in it the genus Grammitis of 
. those authors, His reason for placing so many species 
under one genus is on account of the numerous interme- 
. diate or transition forms, which he Says so pass into one 
_ another that he finds it difficult to define any group of ` 
‘Species as a distinct genus in the manner that Presl and 
. Others had done. Notwithstanding this, however, he finds 
it quite possible to divide the genera into sections and sub- 
sections, of which he gives an elaborate synoptical table. 
He first divides the 268 species, according to their veins, 
— being free or anastomose. Those with free veins are ` 
placed under four Sections, and those with anastomose | 
. veins in thirteen sections. These sections and sub-sections 
(which are numerous) in most cases bear the names that 
. designate the genera of Presl and others, and consequently ` 
