. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. MARATTIACEAE 515 group, to the character of tapetum (Fig. 284 e), and the rule appears to be that the whole tapetum is extra-archesporial in its origin. The figure represents in radial section a sporangium which has arrived at the. Fig. 2S4. Angioptcris euecta, Hoffni. A = part of a young sorus seen in surface view from with- out. B = vertical (radial) section of a sporangium such as would be seen on cutting the sporangium (/>) in Fig. A along the line indicated. C = vertical section of an older sp
. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. MARATTIACEAE 515 group, to the character of tapetum (Fig. 284 e), and the rule appears to be that the whole tapetum is extra-archesporial in its origin. The figure represents in radial section a sporangium which has arrived at the. Fig. 2S4. Angioptcris euecta, Hoffni. A = part of a young sorus seen in surface view from with- out. B = vertical (radial) section of a sporangium such as would be seen on cutting the sporangium (/>) in Fig. A along the line indicated. C = vertical section of an older sporangium, showing genetic grouping of cells. Z> = apex of an almost mature sporangium seen from above ; such a section as along the line x, x, in Fig. E. J5'=verticai section of a sporangium with spore-mother-cells ; the tapetum is marked x. F= transverse section of an almost mature sporangium. All X 200. stage of complete division of the sporogenous mass, and in which the spore-mother-cells are about to separate and round themselves off, prior to the tetrad-division. From such sporangia it is possible to compute the average number of spore-mother-cells, and for this purpose a number of countings have been made. In radial sections the average of the countings gave 59, say in. 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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