EMBRYOGENY OF THE PTERIDOPHYTES 669 
it as possible, it could not be done ‘more exactly than is shown in. Sade- 
beck’s drawings (Fig. 214, p. 393): ome octant enlarges and. thrusts the 
less active octants aside; and its central angle immediately becomes one 
of the angles: of the pyramidal initial, which then continues to segment in 
a sequence of which the original octant walls were the first terms. The 
succession of the cleavages is shown diagrammatically in Fig. 357 a and B. 
The necessary consequence is an appearance in section accurately shown 
in Fig. 358 a, in which it- will be seen that the apical segmentations 
conform with great exactitude to those shown in the diagram. 
Fic, 358. 
Drawings of embryos. A, of Zguisetum (after Sadebeck). 3B, of Marsilia (after 
Hanstein). C, of Adiantum (after Atkinson). They all illustrate with accuracy the origin 
of the apical cell of the axis, according to the scheme shown in Fig. 357. 
_ Even in Leptosporangiate Ferns, notwithstanding the influence of a 
large and precocious cotyledon, the same relation of the apical cell of the 
axis to the octant segmentations may be observed. It is accurately shown 
in Hanstein’s drawing of the embryo of Marszlia salvatrix (Fig. 358 8), 
where the apical cell with its first segment directly adjoins the octant-wall. 
It is equally clear in Campbell’s Fig. 178 F1 for Onoclea sensibilis, while 
Fig. 358 c, after Atkinson, showing the embryo of Adiantum, indicates the 
same cleavages there also, Thus, even in embryos where there is a single 
initial cell, that cell is carved out so as to be in the point nearest the centre 
of the epibasal hemisphere that is consistent with their mode of segmen- 
tation. In the Marattiaceous Ferns, where there is no constant single initial 
at the apex of the stem, the matter is not so clear; but Fig. 292 leaves no 
room for doubt that the position of the apex of the stem is substantially 
the same. In the Ophioglossaceae the segmentation in the embryo has 
not been accurately made out, but sufficient is known to show that in 
1 Mosses and Ferns, p. 322. 
