. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. SPORE-PRODUCING MEMBERS 313. Fig. 158. d, 2,/"= sections radial, tangential, and transverse of mature sporangia of Lycopodinm Selago. g, k, i= similar sections of mature sporangia of Lycopodinm phlegmaria. X 12. tissue also as tapetum. The dehiscence is along a transverse line, and the preparation for this is already indicated at the distal end in Fig. 157 d, d. Meanwhile, the sporogenous group within, in the formation of which the whole products of the archesporium are involved, has been subject
. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. SPORE-PRODUCING MEMBERS 313. Fig. 158. d, 2,/"= sections radial, tangential, and transverse of mature sporangia of Lycopodinm Selago. g, k, i= similar sections of mature sporangia of Lycopodinm phlegmaria. X 12. tissue also as tapetum. The dehiscence is along a transverse line, and the preparation for this is already indicated at the distal end in Fig. 157 d, d. Meanwhile, the sporogenous group within, in the formation of which the whole products of the archesporium are involved, has been subject to repeated cell-division: its cells finally separate, round themselves off, and all of them, as a rule, undergo the tetrad-division. In the mature sporangium the form is less strongly curved in L. Selago than in many other species, while the stalk is a relatively narrow one. The general proportions, as well as the imperfect protection of the sporangium afforded by the rather narrow sporophylls, are shown in Fig. 158 d, e, f. The type of sporangium thus described for L. Selago, with its single row of archesporial cells, relatively narrow stalk, and imperfect protection while young, appears to be character- istic, with relatively slight modifications, of the sub-genus Urostachya : other species of the sub-genus which have been examined, viz., L. dichotomum, Jacq., carinatum, Desv., niimmularifolium, Blume, and Phlegmaria, L., are all alike in showing an archesporium consisting of a single tangential row of cells, though the number of these in the row may vary; the simplest case observed was that of L. Phlegmaria, where the single series consisted of certainly not more than five cells, and perhaps of less. The further development in these species was also the same as in L. Selago, though the proportions were different. In L. dichotomum, however, there is the peculiarity that the sporangial wall is found to be more massive, consisting of 4-7 layers. Putting such differences aside
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