WHAT HAPPENED TO THE SEED-FERNS?

THE flower (which is essentially a special arrangement of the fertile parts) may then have arisen in more than one group, and it is interesting to inquire further into the history of some of the organs of which it is composed. The stamen of a modern flowering plant is nearly always a simple structure consisting of a single stalked anther, but there are a few cases, such as the Castor-oil plant, in which the stamens are much branched. It is tempting to regard this as a primitive character, recalling the branched pollen-bearing organs of various Mesozoic plants. Other fossil male organs are known in which each stalk bears a tuft or tassel of anthers, and these may have given rise by reduction to the ordinary stamen with one anther. The carpel or closed seed-case is so characteristic of living flowering plants that it has given the name Angio-sperm (hidden seeds) to the whole group.

Now in the same Yorkshire beds which yield the cliff-roses some small fossils have been found looking rather like bunches of currants, and on investigation each ‘currant ‘proves to be a carpel containing seeds. These fossils, which have been named Caytonia, are quite unlike any known flowering plant :

are we then to regard them as an early isolated group of Angiosperms, or is this another case in which a classification based solely on recent plants proves a stumbling-block when we come to consider the fossils? We must not allow our own imperfect terminology to entangle us, and ‘angiospermy ‘(the possession of a closed carpel) may well have arisen in Jurassic times in groups now extinct which we cannot really call angiosperms.

None the less, though we do not yet know sufficient about this Jurassic carpel-bearing fossil Caytonia to give an answer, we cannot help asking ourselves whether it may not be on the line which led to the modern flowering plants. Whence was Caytonia derived? There are several points, not only in the structure of the carpel and seeds, but in the associated branched stamens with tufts of anthers, which are comparable with some of the seed-ferns of the Palaeozoic. Moreover, in the early Mesozoic rocks of South Africa (earlier than those in which Caytonia has been found) there are other fossil reproductive organs which, while recalling Caytonia, are still more like the older seed-ferns. These organs are associated with leaves known as Dicroidiwn, already referred to above as characteristic of the southern flora in the Triassic period.

The evidence therefore suggests that the one great group of Palaeozoic plants which survived in a flourishing condition into the Mesozoic era was the seed-ferns; that though the changed conditions in the north may have exterminated most of the Coal Measure forms, the somewhat different southern families continued to evolve and later invaded the northern hemisphere; and that the modern flowering plants may have arisen from early Mesozoic seed-ferns.

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