LEAF-ARCHITECTURE AS ILLUMINATED BY A STUDY OF PTERIDOPHYTA. 679 



across the frontal face of the leaf, as in Todea. Thus there is nothing in the leaf 

 of Angiopteris, as an example of the Marattiaceae, incompatible with what is seen 

 elsewhere in Ferns ; but certain features point a comparison with Seed-Plants. 



Opliioglossacese. 

 The cotyledon of Helminthostachys has been depicted by Lang.* The ternate 

 form of the leaves is shown, but no special attention was paid to their venation. 

 Dr Lang has kindly supplied to me three juvenile leaves (either cotyledons or second 

 leaves) from his Eastern collections, from one of which fig. 12 was drawn. The 

 deeply ternate lamina has a venation which is evidently a scorpioid sympodial 

 dichotomy. The junction of the pinna-supply at the base of the left-hand pimia is 

 the lower, and the right-hand the upper ; and it will be noted that the insertion of 



Fig. 12. — A juvenile leaf of Helminthostachys, probably an actual cotyledon. 

 From the collection of Dr Lang. ( x 4.) 



the main shanks in the distal lobe alternate, the lowest being on the left, thus 

 alternating with the right-hand pinna. In fact, the whole structure is disposed on 

 the same plan as in fig. 1, g, of Osmunda. The chief differences are that the sinus 

 between each pinna and the terminal lobe in Helminthostachys is deeper, and that 

 the basal pinna in fig. 1, g, of Osmunda is to the right; this character is, however, 

 inconsistent in Osmunda. We have seen that in Osmunda the stage of fig. 1, g, is 

 only arrived at relatively late, being preceded by smaller leaves with regular 

 dichotomy. Thus Helminthostachys steps direct into a position that is only 

 secondary and derivative in Osmunda. The latter may then serve to interpret the 

 real nature of the venation in the former, and the comparison justifies its recognition 

 as a scorpioid sympodium, although the preliminary stage of equal dichotomy is not 

 actually shown in its first leaves. 



The mature leaf of Helminthostachys has a venation with a strongly marked 

 midrib in each segment, from which veins arise in pinnate fashion, forking once, or 



* Ann. of But., vol. xvi, pi. ii, fig. 61 ; and by Campbell, Eusp Fern*, figs. 10, 45, 78. 



