. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. 668 CONCLUSION This general principle may be illustrated by comparison of certain of the figures quoted in Part II. Thus in Fig. 185 a, b (p. 348) of Lycopodium Phlegmaria the apical point T coincides very nearly with the intersection of octants, though it appears unsymmetrical owing to unequal growth caused by the precocity of the cotyledon (c), but it is righted by the appearance later of the second leaf (Figs. 185 c, d). It cannot be doubted that the case of L. Selago is very similar, though the •a
. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. 668 CONCLUSION This general principle may be illustrated by comparison of certain of the figures quoted in Part II. Thus in Fig. 185 a, b (p. 348) of Lycopodium Phlegmaria the apical point T coincides very nearly with the intersection of octants, though it appears unsymmetrical owing to unequal growth caused by the precocity of the cotyledon (c), but it is righted by the appearance later of the second leaf (Figs. 185 c, d). It cannot be doubted that the case of L. Selago is very similar, though the •a detailed study of cleavages is not yet to hand (Fig. 183, p. 346). Fig. 186 (p. 349) of L. annotinum shows the coincidence of the apex (s) with the cleavage-wall (11) very plainly indeed. As the cleavages have not yet been traced in the more aberrant L. cernuum, it is impossible to say more than that the ob- served facts do not preclude a similar origin of the axis, which comparison with Phylloglossum makes probable (p. 353). In Selaginella spinulosa (Fig. 190, p. 357) a comparison of the stages a, c, d clearly shows that the small-celled tissue of the apex of the axis includes the intersecting octant walls. A similar origin of the axis to that in Lycopodium and Selaginella spinulosa may be traced for Isoetes, notwithstanding the ab- sence of a suspensor and the small size and late definition of the apex (Fig. 191, pp. 359- 360). The case of S. Martensii is interesting for comparison, since there is a single initial cell, a condition which is probably derivative as compared with that of 5. spinulosa, with its small-celled meristem. Pfeffer's drawingsl demonstrate how this originates with the octant wall forming one of its lateral faces; in fact, at the nearest point to a central position compatible with its existence as a single initial cell. The embryo of Equisetum shows this even more plainly: if a single initial cell is to be carved out of ah epibasal hemisphere of four o
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