. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. FACTORS OF DECREASE 127 Arisariim, and in Najas, %Cmlinia, can hardly be ascribed to any other source than the fusion of the pollen-sacs, separate in the ancestry, into a single loculus. Thus in the androecium of Angiosperms. and occasionally. *,„1:jl St (fpi t, & Wki (LJ^^3rff--si Fig. 69. Juniperus communis. I., summit of a male flower seen from above. 5^, the uppermost staminal whorl of these stamens; st2, the second staminal whorl shows on each stamen two pollen-sacs, and the indication of a l
. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. FACTORS OF DECREASE 127 Arisariim, and in Najas, %Cmlinia, can hardly be ascribed to any other source than the fusion of the pollen-sacs, separate in the ancestry, into a single loculus. Thus in the androecium of Angiosperms. and occasionally. *,„1:jl St (fpi t, & Wki (LJ^^3rff--si Fig. 69. Juniperus communis. I., summit of a male flower seen from above. 5^, the uppermost staminal whorl of these stamens; st2, the second staminal whorl shows on each stamen two pollen-sacs, and the indication of a lamina, /; sr"3, the third staminal whorl, of which only the tips of the lamina; of two stamens are seen : each of the stamens of this whorl had three pollen-sacs, not shown in the figure. II., the same in longitudinal section. III., the same in transverse section. There is evidence here of reduction of the lamina, and effusion of the pollen-sacs. (After Goebel.) in the gynoecium, a fusion of sporangia is recognised, resulting in a reduc- tion in their number. The apex of the male flower in Junipents communis has been quoted by Goebel as a probable example of fusion of pollen-sacs (Fig. 69). In certain Pteridophytes the grouping of the sporangia is often such as to suggest a previous fusion ; but this has not been proved on developmental or comparative grounds for any one case, and the question must be left open for discussion on grounds of general probability whether the synangial state in any individual case has been the result of fusion, or of septation with incomplete separation of the sporangia : obviously the synangial structure would be compatible with either origin. Whatever the final decision for the Pteridophyta may be, it is clear that fusion of sporangia originally separate has actually occurred in Flowering Plants : it is therefore a factor which must be regarded as a possible explanation of all synangial states. (g) Abortion, partial or complete, of sporangi
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