. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. EMBRYOLOGY 359 other parts originate from the epibasal tier: the cotyledon with its ligule is the first part to be organised: it is followed soon by the first root, which arises at the opposite side of the epibasal tier to the cotyledon (Fig. 191 c, d, e, f). Between these parts a slight depression is formed, and it is surrounded by a semicircular ridge: within this the apex of the axis is at last organised, and it soon gives rise to the second leaf, which. Fig. 191. Jsoetes echinospora, var. Braunii,
. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. EMBRYOLOGY 359 other parts originate from the epibasal tier: the cotyledon with its ligule is the first part to be organised: it is followed soon by the first root, which arises at the opposite side of the epibasal tier to the cotyledon (Fig. 191 c, d, e, f). Between these parts a slight depression is formed, and it is surrounded by a semicircular ridge: within this the apex of the axis is at last organised, and it soon gives rise to the second leaf, which. Fig. 191. Jsoetes echinospora, var. Braunii, Dur. X 365. A =an arcbegonium. B=s. two- celled embryo within the archegonium. D, E, ^=three successive horizontal sections of a somewhat advanced embryo; i?=root; ££=cotyledon ; j/=stem; /=ligule. x 175. C=median longitudinal section of a young embryo; /=ligule. X 200. G=median section of a young sporophyte with second leaf, ^2, already formed; r%=second root; s*=stem apex, x 150. (After Campbell.) faces the cotyledon: the very exiguous apical cone lies between them (Fig. 191 g). And so the shoot is established, bearing successive leaves with spiral arrangement, and successive roots, of which the second is below the base of the second leaf. Comparing this apparently divergent embryogeny with that of the Lycopods above described, if the whole embryo be imagined inverted in its orientation relative to the archegonial neck, and their suspensor be imagined entirely away, then the two embryonic tiers may be com-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Bower, F. O. (Frederick Orpen), 1855-1948. London, Macmillan and Co. , Ltd.
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