666 CONCLUSION 



undergoes octant-division : l the succession of the divisions is not always 

 the same, but as a rule there is first a basal wall (i;, B) parallel to the 

 wall i, i, which divides the embryonic cell into hypobasal and epibasal 

 tiers, and this is followed by quadrant and octant walls at right angles 

 (Fig. 355 Q, Q; o, o), which divide each of those tiers into quarters. The 

 result is a body which shows in many cases, by its elongating form, that 

 there is a distinct polarity : its form and constitution are illustrated by 

 diagrammatic figures (Fig. 355 I. n), in which the suspensor is cross- 

 hatched, the hypobasal tier dotted, and the epibasal tier left clear. Such 

 a scheme will serve for all Pteridophyte embryos with suspensor which 

 have been fully elucidated. 



Turning to embryos without a suspensor, the segmentation of the whole 

 zygote into octants is similar to that seen above in the embryonic cell, 

 where a suspensor is present, but with the suspensor completely omitted 

 (compare Eqitisetum, Fig. 214; Ophioglossaceae (excl. Botr. obli</i<inn}, 

 Figs. 260, 261, 261; Isoefes, p. 350; and all Filicales). It is represented 

 diagrammatically in Fig. 355 in., where again the hypobasal region is dotted 

 and the epibasal left clear. Without attaching undue importance to the 

 cell-cleavages themselves (for they resemble those in certain quite distinct 

 bodies, such as capitate hairs), they may be held as indications of the 

 growth, and, what is more important, of the polarity already denned in 

 the body of the embryo. The first indication of the existence of this 

 polarity is given by the position of the first segment-wall (i, i), or B, B 

 in cases where a suspensor is absent ; and it may be shown that in all 

 fully investigated cases the apex of the axis has a definite relation to that 

 first wall. It appears at the centre of the epibasal hemisphere, that is, 

 in close relation to the intersection of its octant walls : the point is 

 marked (x) in the diagrammatic Figures 355 i., n., in. 



It should be clearly understood that however constant the orientation 

 of the embryo may be in cases where a suspensor is present, the orienta- 

 tion is not constant in the type without a suspensor : in these the apex 

 of the axis bears no necessary or constant relation to the axis of 

 tin: archegonium, either for Archegoniate plants at large, or for the 

 several phyla of them, or yet for genera or even for individuals. As a 

 matter of observation, the orientation of the definitive shoot is initiated 

 sometimes with its apex towards the neck of the archegonium (compare 

 Fig. 214 of Ei/uisctinii, and Figs. 260-262 of the Ophioglossaceae, with 

 the diagrammatic Fig. 356 in.); or obliquely to one side, e.g. Lepto- 

 sporangiate Ferns (compare Hgs. 14, 15 with diagrammatic Fig. 356 n.); or 

 away from it (as in Marattiaceae, compare Fig. 292 with the diagrammatic 



"Compare especially Fig. 190 ot .s'< / ^piiiiiu>,i\ ;ilso, though less clearly, I'feffer's 

 drawings of .V. Martt-nsii, Hansicin'.s Abliandl., vol. i. Taf. 2, 3; Treub's drawings of 

 Lye, riili'^nntrni ( Kig. 185), but more fully in ./////. /tinf. Hot. />////., vol. v. Taf. xxiii., 

 \\iv., and Bruchmann's drawings of / y, . ,l,r<\itnin and aiinotinnin (1'ig. 186) ; but more 

 fully in Bruchmann's own memoirs ijuoled above. 



