863 IMPKOVEMSNT IN TEIE AKRANaEMENT OF FERKS. 



Tribes : 



1. Adiantinse. 



Sori marginal. 



2. Aspleniiuas. 



Sori scattered, elongated. 



3. AspidiiDa3. 



Sori scattered round. 



T have not noticed, in tins arrangement, a group called Parkeriacra), 

 and usually enumerated in what I have called the order Osmundaceco. 

 My reason is, that this very small tribe seems to me to be founded on 

 unsatisfactory data. There are but two genera. In one of these 

 (Ceratopteris) the annulus is so nearly complete, being also vertical, 

 that there is little pretence for placing it among the Osmundacese. la 

 Parkeria the annulus apparently occupies a very small space on the 

 sporangium, but as far as it goes it has the jointed appearance very 

 perfectly, and in Bauer's figure it is a little more extended, and shows 

 more trace of a baud round the sporangium than in Hooker's own 

 figure. The aquatic habit and the very curious spores common to both, 

 forbid any separation of Parkeria from Ceratopteris. I conclude, there- 

 fore, that though exhibiting transition characters, such as occur every- 

 where in nature, they ought to stand among the completely annulate 

 ferns, and, on account of the indefinite naked sori on the veins, should 

 be placed in Plemionitidinse. This is the only tribe which I have 

 thought it necessary to add to those already characterised, but it seems 

 to me well distinguished, and required to complete a system of analogies 

 among the tribes which is very pleasing and interesting. It was iiideed 

 noticed as a sub-tribe by Presl. 



The numerous proposed genera of Polypodiiiiae, most of which are 

 entirely abandoned by Sir W- J. Hooker, present great difficulties. I 

 have myself no doubt of the propriety of admitting as characters the 

 more definite distinctions of venation, and indeed where there is any 

 distinct natural group, we should gladly seize upon any tolerable techni- 

 cal character to set it apart under a distinct name, bat some of the pro- 

 posed genera rest on so slight a foundation that they cannot be sustained. 

 A careful revision of this part of the subject by some writer possessing 

 extensive materials and cautious judgment, not so much afi-aid of 

 transitional forms or so strict in his adherence to the great old estab- 

 lished genera often equivalent with tribes as now understood, as Hooker, 

 yet prepared to exercise a rigid scrutiny into the merits of proposed 



