. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. 98 STERILISATION in homospbrous and in heterosporous forms; the sterile cells may be- functional sometimes only as transitory, nourishing cells; or they may persist as permanent tissue, forming in some cases partial, in others even complete septa. The converse case, viz. the conversion of cells normally sterile into, fertile cells, is a much less common phenomenon, though instances of it have been observed. This change is not to be confounded with the formation of whole organs of propagation, such as
. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. 98 STERILISATION in homospbrous and in heterosporous forms; the sterile cells may be- functional sometimes only as transitory, nourishing cells; or they may persist as permanent tissue, forming in some cases partial, in others even complete septa. The converse case, viz. the conversion of cells normally sterile into, fertile cells, is a much less common phenomenon, though instances of it have been observed. This change is not to be confounded with the formation of whole organs of propagation, such as sporangia, in places, where they do not normally exist: what is here meant is the change in. Fig. 55. Casuarina Rumphiana, Mig. Median section of the nucellus of an ovule, with the group of sporogenous cells shaded. X285. (After Treub.). 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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