. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. AS SEEN IN PTERIDOPHYTA 93 margin. Fig. 47 illustrates how the series of cells of the archesporium is continuous both upwards and downwards beyond the limit of its fertility : this indicates a probability that its marginal limitation has been due to sterilisation, a view which is strengthened by comparison with Sphagnum (Fig. 48); for there the archesporium is in the form of a complete dome : tcm docM? £. Oanaca elliptica, Smith. Drawings illustrating partial septations of the sporangiu
. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. AS SEEN IN PTERIDOPHYTA 93 margin. Fig. 47 illustrates how the series of cells of the archesporium is continuous both upwards and downwards beyond the limit of its fertility : this indicates a probability that its marginal limitation has been due to sterilisation, a view which is strengthened by comparison with Sphagnum (Fig. 48); for there the archesporium is in the form of a complete dome : tcm docM? £. Oanaca elliptica, Smith. Drawings illustrating partial septations of the sporangium. A, tangential section through three sori, showing the loculi in ground plan : the septa are often thin, so that pairs of loculi are in close juxtaposition ; the loculi marked (x) are large, and show one or more partial septa. X 20. B, C, D, £, show such loculi with partial septa in greater detail : in D and E it is difficult to decide whether the tells marked (?) will develop as tapetum or as spore-mother-cells. X 150. a sterile condition of the cells at its apex would give a barrel-shaped archesporium, as is seen in the Bryineae. Thus it will appear that any evidence of sterilisation in the Musci is less direct than that in the Hepaticae. Evidence of sterilisation of potential sporogenous cells is common in the homosporous Pteridophyta: and, as in the Bryophytes, the function. 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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