626 GENERAL COMPARISON OF THE FILICALES 
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Examples illustrating that this has actually occurred have already been seen 
in the living Marattiaceae; while Angiopteris and Marattia have upright 
and radial stocks, that of Danaea becomes oblique or even prone as it 
grows older, and Kaulfussia, with its longer internodes, is a creeping form. 
In all of these, however, where the embryo is known, the shoot is in the 
first instance erect. It seems plain that there has been a transition from 
the upright and radial to the prone and dorsiventral type. 
In the living representatives of those sequences of Ferns which culminated 
in the Leptosporangiate group dorsiventrality is more common, and it is 
already seen to be prominent in such early types as the Schizaeaceae, 
Gleicheniaceae, and Matonineae, though the Cyatheae and Dicksonieae are 
strongly radial. There is some reason on anatomical grounds for thinking 
that the living Hymenophyllaceae show in their radial types a recovery of 
Fic. 347. 
Portion of the leaf surface of a seedling of asplenium serpentinz, showing how 
dichotomy accompanies the marginal growth. xz1g90. To the left a diagrammatic 
representation of the same. (After Sadebeck.) 
* 
the upright shoot from the creeping rhizome, and this may have occurred 
in others of the Leptosporangiate Ferns. However this may be, the 
Leptosporangiate Ferns show radial and dorsiventral development so 
intimately intermixed that it is more difficult in them to trace the probable 
evolutionary relations than in those groups which are clearly indicated as 
the most ancient. But taking the facts over all, it appears reasonably 
probable that the primitive shoots of Ferns were radial, and that dorsi- 
ventrality was here as elsewhere derivative.! 
In some Ferns the axis remains unbranched, as in the Marattiaceae. 
In others dichotomous branching of the axis is seen to occur, and there 
is reason to recognise this as a primitive mode of increase, since it occurs 
characteristically in relatively early forms, such as in Lygodium, in the 
1Mr. Tansley remarks very pertinently that ‘‘dorsiventrality is not very common in 
fern steles, in spite of the prevalence of creeping rhizomes” (New Phytologist, 1907, p. 112). 
To those who hold that vascular structure follows rather than dominates development this 
is important evidence in favour of a primitively radial construction of the Fern-shoot. 
