782 TRANSACTIONS OP SECTION K. 



ranked by Sir W. Hooker, and that it occupies an important intermediate posi- 

 tion, throwing light upon the phylogeny of certain ferns. Its stclar character, 

 only slightly removed from solenostely, its undivided leaf-trace, its simple forked 

 venation, occasional dichotomy of axis, absence of flattened scales, absence of a 

 true indusium, its sorus initially simple but showing later a 'mixed' character, 

 the segmentation of the sporangium, its thick stalk, oblique annulus, indeter- 

 minate stomium, and tetrahedral spores collectively indicate it as relatively 

 primitive. It shows resemblances to all the great series of Simplices, but not to 

 any one of them so clearly as to point to close affinity. Its position is probably 

 in relation to the Gleicheniacere and Sehizreacea?, and perhaps specially to th3 

 latter. On the other hand, the ' mixed ' character of the sorus, together with 

 many of the features above named, points towards the Pterideae. But these have 

 a vertical annulus, while that of the Plagiogyria is oblique. This distinction is, 

 however, bridged over by the fact that in Cryptogrammc (with which Plagiogyria 

 has been associated systematically by Diels') traces of an oblique annulus are 

 clearly seen. The sporangia are far from uniform in their details; the series of 

 cells of the annulus may be at times irregular or broken ; isolated cells of the wall 

 may be indurated like cells of the annulus; sometimes the annulus may appear 

 vertical and interrupted at the stalk, but at others it can be traced clearly past 

 the insertion of the stalk. These facts indicate Cryptogramme as in an unstable 

 condition between the oblique and the vertical annulus, and suggest that a real 

 transition has occurred from the former as primitive to the latter as a derivative 

 state. 



If this be so, we have outlined a great phyletic sequence from some type of 

 Simplices, allied in the neighbourhood of the Schiza&aceee and Gleicheniacese 

 to the whole sequenece of the Pterideae, which have always been regarded as a 

 relatively primitive series. And this transition appeals to have been direct 

 from the 'simple' to the 'mixed' i>orus without any 'gradate' condition inter- 

 vening. 



Another somewhat similar sequence may be also recognised, but in this case 

 leading to the 'gradate' series of Cyatheaceae. It starts from the genus Lopho- 

 soria, represented by the single species //. prvrtiata (Pr.) designated by Christ 

 Alsophila quadripinnata (Ginel.), C.Chr., and long merged in the genus Alsophila, 

 from which it should be separated on various grounds.. It is a low-growing 

 tree-fern, with handsome leafage and profure production of runners from the 

 base of the stock. The young parts are covered by hairs, scales being absent. 

 The stem shows solenostelic structure, especially in the runners, where the leaves 

 are not crqwded. The sorus is superficial and naked, of the Gleicheniaceous type, 

 nil the sporangia arising simultaneously ; the annulus is oblique, but the de- 

 hiscence is lateral, and the spores approximately G4. Such characters point in 

 the direction of Gleiclienia, and especially to the more advanced types of Mir- 

 tensia, such as (r. dichotoma and pectinata. These, with (,'. fiabellata as a rela- 

 tively primitive species, form a sequence in which increase of anatomical com- 

 plexity towards solenostely goes parallel with increase in number of sporangia in 

 the sorus and decrease in size and spore-output of individual sporangia. There 

 is, however, a decided break between the sporangia] details in Gleichenia and 

 those of Lophosoria. It is not suggested that Lophosoria is a further term in 

 this series ; but it is suggested that the mechanical possibilities of further elabora- 

 tion of the sorus along the lines of G. pcrtinata with close-packed sporangia and 

 median dehiscence were exhausted; that a new start was made by a race which, 

 while maintaining the main characters of Gleicheniacece., adopted lateral dehiscence 

 and finally a gradate sequence of sporangia; and that Lophosoria is perhaps the 

 most primitive living example of that type. 



On the other hand, the relation of Lophosoria to Alsophila is obvious; but 

 Alsophila bears scales as well as hairs, though' the sorus is naked. In Hemitelia 

 the scales, in the form of an incomplete indusium. imperfectly protect the sorus, 

 while in Cyathea the specialisation of the scale for this purpose is perfected in 

 the indusium. Such protection became all the more necessary as the ' gradate ' 

 development was assumed. 



It would further appear, if this sequence is correct, that the prostrate position 



1 Engler and Prantl. Pflanzenfam., T., 4, p. 279. 



