98 Studies in the Morphology of Spore-producing Members. 



and to their arrangement in the sorus. Thus the position of the 

 annulus, which has played so important a part in classification, has 

 been placed upon a footing of adaptation. 



Estimates of numerical output of spores per sporangium have been 

 made with a view to illustrating the relation of the Eusporangiate and 

 Leptosporangiate ferns in this respect. The estimated output in the 

 Marattiaceae has been shown to be high ;* that of the Polypodiaceae 

 is sixty-four or less. The result of numerous countings is to show 

 that, of all Leptosporangiate ferns, Gleichenia approaches most nearly 

 to the Marattiaceae (Gl. flabellata may produce over 800 per sporan- 

 gium) ; Osmunda may have over 500, and Lyg odium 256. The most 

 interesting results were derived from the Hymenophyllaceae, in which 

 Hym. tunbridgense may have over 400, while species of Trichomanes 

 may produce as few as thirty-two per sporangium. These results, 

 when taken with those derived from the filmy Todeas, make it seem 

 probable that the filmy habit is a condition leading to reduction of 

 output per sporangium, and indicate that the Hymenophyllacea3 are 

 a derivative series of reduction. 



A most important commentary upon the classification proposed is 

 derived from comparison of the antheridia, which Heimf found to be 

 the most dependable part of the Gametophyte for comparative pur- 

 poses. He recognises two types according to their dehiscence : the one 

 type includes, with the exception of two genera of Schizaeaceae, our 

 Simplices and Gradatae, while the other includes the Mixtae. I can 

 only regard this correspondence of parts, so aloof from one another as 

 the antheridium and the sporangium, as establishing the relations of 

 the Simplices and Gradatge upon a firmer footing ; the facts also give 

 substantial support to the distinction of the Gradatae and Mixtae. 



The effect of the observations and comparisons in this memoir is 

 rather confirmatory of the current classifications than disturbing. The 

 divisions suggested would supersede those of Eusporangiatae and Lep- 

 tosporangiatae, though these terms would still be retained in a 

 descriptive sense. If the sub-orders Osmundaceae, Schizaeaceae, and 

 Marattiaceae be transferred from the end of the Synopsis Filicum to 

 the beginning, and grouped with Gleichenia and Matonia, we have the 

 " Simplices " before us. The Gradatae include the Cyatheaceae, Dick- 

 sonieae (Excl. Dennstaedtia), Hymenophyllaceae, and Loxsomaceae, 

 sequences probably of distinct descent, and, in my view, derivative 

 from some prior forms such as the Simplices ; and in the arrangement 

 of Sir Win. Hooker they hold a position following on the Gleichenia- 

 ceae. The family of Dennstaedtiinae, founded by Prantl to include 

 Dennstaedtia and Microlepia, also has its place here, but it leads on by 

 intermediate steps to undoubtedly mixed forms such as Davallia, 



* 1 Studies,' No. 3, p. 60. 

 t ' Flora/ 1896, p. 355, &c. 



