XI THE HOMOSPOROUS LEPTOSPORANGIAT^E 375 



Laccopteris, which occurs in early Jurassic beds, concludes that 

 the two genera are very near each other if not identical, and 

 represent the earliest forms of the Cyatheacea^, and that Matonia 

 is the last remnant of a group which is now in process of 

 extinction. 



TJie PolypodtacecE 



The Polypodiaceae may very aptly be compared to the 

 stegocarpous BryinejE among the Mosses, inasmuch as like that 

 group they give evidence of being the most specialised members 

 of the order to which they belong, and compose a very large 

 majority of the species. Most of them agree closely in their 

 structure, which has been given in detail, and will not be 

 repeated here. With very few exceptions the structure of the 

 prothallium and sexual organs is like that of Otioclea, but one 

 or two variations may be mentioned. In Vittaria, Goebel ' 

 has found a type of prothallium recalling that of Hyvienopliylluin, 

 both in its large size and extensive branching. Its earlier 

 stages show the ordinary development, but it later branches 

 extensively, and, like Hyinenophyllinn, numerous groups of 

 archegonia are formed upon one prothallium. Bodies resem- 

 bling the oil bodies of Liverworts are also met with in this 

 genus. The sexual organs closely resemble those of the 

 Polypodiaceai, but the antheridia have a well-marked stalk, 

 something like that found often in the Hymenophyllacese. 

 Another aberrant genus is Ceratopteris, which differs so much in 

 several respects that it has sometimes been regarded as the 

 type of a separate family.' It is, unlike all other homosporous 

 Ferns, a genuine aquatic, and no doubt this anomalous habit 

 has something to do with its peculiarities, especially the im- 

 perfect development of the ring of the sporangium, which, 

 according to Hooker,^ is often met with. 



The prothallia show some peculiarities as well. Thus, while 

 the early stages are like those of other Polypodiaceae, the arche- 

 gonial meristem is developed, not from the apex of the 

 prothallium, but laterally, and quite independent of the original 

 growing point, which is pushed to one side. The antheridia 

 are of the polypodiaceous type, but project less than in the 

 other forms. The sporangia are very large, but correspond in 

 their development with that of the other Polypodiaceae:. 



1 Goebel (9). ^ j^ny (6). 3 Hooker (i), p. 174. 



