. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. i'. 404 SPHENOPHYLLALES. A. SPHENQPHYLLEAE were united at the base into a narrow sheath or collar surrounding the axis. The transition to the strobilus is plainly seen at the lower limit of the large specimen from the Brussels Museum, described and figured by Kidston : towards the upper limit of the specimen, where the sporangia cease, the axis is continued in the vegetative manner, with longer internodes. These facts plainly point to the absence of a highly differentiated strobilus, and the existence
. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. i'. 404 SPHENOPHYLLALES. A. SPHENQPHYLLEAE were united at the base into a narrow sheath or collar surrounding the axis. The transition to the strobilus is plainly seen at the lower limit of the large specimen from the Brussels Museum, described and figured by Kidston : towards the upper limit of the specimen, where the sporangia cease, the axis is continued in the vegetative manner, with longer internodes. These facts plainly point to the absence of a highly differentiated strobilus, and the existence in this species of a " Selago" condition, where the fertile region is a mere zone on a continued axis. Not only does S. majus stand as yet alone in the genus by the indefiniteness of its cone, but also in the character of its sporangiophores. One of these is borne near to the base of each forked sporophyll (Fig. 222) : the sporangia, which are 4-6 in number, but usually four, are grouped round a central attachment; and though no elongated pedicel can be seen, still the fact that when they are removed from the bracts they still remain united in groups of four to six indicates that gmmmatic sketch of the arrange- they had a common base. In favourable cases Stdston.) ' e sporangia' ter Kidston has been able to demonstrate that a radial line of dehiscence is clearly marked, corresponding in position to that of the synangium of Psilotum, to which the whole structure shows a remarkable resemblance. As a last type, and not the least remarkable of this variable genus, may be mentioned the fructification of .S. fertile, recently described by It is characterised by the fact that both the " dorsal and ventral lobes are fertile," by which is meant that the bract bears sporangia as well as the sporangiophore, which it subtends. Dr. Scott remarks that this is " more probably due to special modification th^n to retention of a primitive ; With
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