214 SYMMETRY OF THE SPOROPHYTE 
succeeding leaves may vary, as was already noted by Hofmeister. He 
stated specifically! that “the similarity in the development of the different 
species of Ferns does not extend beyond the formation of the rudiments 
of the first frond, and of the first root.” He then proceeded to show 
that whereas in Pyeris aguilina the second frond originates on the side 
of the axis opposite to the first, and distant from it by about half the 
circumference of the stem, in Mephrodium (Aspidium) Filix mas it is 
at a distance of about a third of the circumference”: “the third diverges 
from the second, and the fourth again from the third at about 120 
degrees to the right, so that the fourth stands vertically over the first.” 
Thus the arrangement of the leaves is radial from the first in the Male 
Fern. The same radial character, with varying divergences, has been 
found in other Fern-seedlings: for 
instance, in Vephrodium adilatatum, 
Asplenium marinum, Fteris tremula, 
Osmunda regalis, and Todea superba. 
The leaf-divergence in such cases is 
variable, but approximates to a half, 
or one-third, and it is spiral from the 
first, without dorsiventral tendency. 
This shows that in plants which are 
radial in the mature state the initial 
condition of the recumbent embryo 
does not impress dorsiventrality on the 
seedling. In others, however, where the 
Polypodium vulgare. X6. Median section : ‘ 
through prothallus, and embryo, partly diagram- Mature plant is markedly dorsiventral, 
matic : showing one series only of the distichous : ‘ : 
leaves 44, d, etc. ; R =roots; ap=apex of axis. the dorsiventrality asserts itself early. 
The pyponastic Shoot becomes complctely Among these the case of Polypodium 
vulgare is very instructive, as showing 
that the dorsiventrality of the mature shoot is not a direct consequence 
of the initial procumbent position. The initial embryogeny is as usual: 
the second leaf of the embryo is obliquely on the same side of the 
axis as the first, and as the subsequent leaves are also inserted alternately 
and obliquely on that same side, and the growth of the axis is stronger 
on that same side which faces away from the prothallus, the whole 
shoot becomes inverted by a strong curvature upwards through the 
apical indentation of the prothallus; and thereafter it pursues its horizontal 
course backwards over the top of the prothallus (Fig. 110). It is interest- 
ing to note as a consequence of this that the side of the axis initially 
turned downwards in the embryo becomes the upper side of the dorsi- 
ventral rhizome, owing to the inverting curve: thus the creeping posi- 
tion of the permanent shoot is not merely a direct continuance of the 
initial prone position of the embryo. Other examples might be quoted, 
but this will suffice to show that the dorsiventrality of the mature shoot is 
Fic. r1o. 
1 Higher Cryptogramia, Eng. ed., p. 208. 2 Lic, p. 227. 
