ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 313 



obtained : 1. Cheiropleuria, Platy cerium, and perhaps Neocheiropteris, 

 share with the fern hitherto styled Leptochilus tricuspis (Hook.) C. 

 Chr., an extension of the sorus, with a special vascular supply, spreading 

 in a plane below and parallel with the venation of the sporophyll. This 

 is most extensive in Platycerium and L. tricuspis, and the condition may 

 be described as dipJodesmic. 2. These ferns, in external morphology, 

 venation, anatomy, sorus, and sporangia, are regarded as Dipterid 

 derivatives, and may be grouped phyletically as Dipteroideae. To these 

 may probably be added, later, many Polypodioid ferns, especially 

 Pldehodium, Phymntodes, Nipliobolus, and Drynaria, and some simple- 

 leaved species of Leptochilus. 3. L. tricuspis stands alone in the latter 

 genus in various features, but especially in the diplodesmic character. It 

 «hould, therefore, be removed, and by reviving its old generic name, 

 now merged in Leptochilus, it may be styled Gymnopteris tricuspis 

 (Hook.) Bedd. Of that genus it will be at present the only species. 

 4. A parallel series to the Dipteroideai, but differing in venation, and 

 probably distinct phyletically, is related to Metaxya as its probable 

 source. It includes Syngramme and Elaphoglossum. These may be 

 ■styled the Metaxyoideae. 5. Both of these progressions illustrate 

 advance from circumscribed sori to an " Acrostichoid " spread of the 

 sporangia over the leaf-surface. This runs parallel with changes of 

 leaf-form, disintegration of the vascular tracts, passage from dermal 

 hairs to scales, increasing areolation of veins, and changes of sporangia 

 from the continuous oblique to the interrupted vertical annulus. Since 

 there is substantial parallelism in these various characters of advance, 

 the progressions are firmly established ; but they are constantly dis- 

 tinguished from one another by their venation. 6. The genus 

 Leptochilus, as at present defined, may probably be a composite genus, 

 not a phyletic unity. 7. The " Acrostichoid " condition has been acquired 

 along a very considerable number of distinct phyletic lines. Accordingly 

 Acrostichum connotes not a genus in the sense of a phyletic unity, but a 

 condition or state, which has been arrived at from various distinct 

 sources. 



Leaf-trace in Pinnate Leaves of Ferns.* — R. C. Davie publishes the 

 results of his investigation of the leaf-trace in some pinnate leaves — 

 viz. fronds of South American and Scottish species of Polypodium 

 collected from stations representing very different conditions. The 

 leaf -traces and pinna-traces of these and of species of Aspidium, 

 Polystichum, Bryopteris, Leptochilus and other genera were examined 

 and compared. The author states that the habitat of the fern was not 

 found in any case to influence the type of leaf -trace or pinna-trace. In 

 a few species of Polypodium the habitat was found to have an effect on 

 the number of tracheides in the leaf-trace. The type of pinna-trace is 

 constant within a genus, recognized as such in Christensen's Index 

 Filicum ; the form of the leaf -trace is dependent on the length of the 

 leaf and the size of the pinnre. The form of the adaxial portion of the 

 leaf-trace is constant throughout a genus ; the degree of development of 



* Trans. Roy. Soc. Edinburgh, lii. (1917) pp. 1-36 (1 pi. and figs.). 

 Ju7ie 20th, 1917 Y 



