THE FLOWER APPEARS AT LAST

IT has been estimated that one-third of the species of Mesozoic plants belonged to the cycadophytes, and even if this includes a number of strange forms whose real affinities are uncertain, we may also say that the group exhibits as wide a range of structure as is to be seen in the seed-ferns of the Palaeozoic. Though some of them bore cones, the fructifications of others may rightly be described as flowers.

In the Jurassic rocks of the Yorkshire coast one may often find fossils which look something like a Magnolia flower; they are known locally as Cliff-Roses—one of the very rare instances in which a fossil plant has been given a popular name—and their scientific name is Williamsonia. They usually have an outer whorl of large leafy bracts which look like sepals or petals, surrounding either a whorl of stamens or a central seed-bearing cone. In some related forms seeds and stamens are found together in the same flower. The seeds, though surrounded by protective scales, were exposed at their tips and not enclosed in a carpel or seed-case as in the familiar flowering plants of to-day. That is to say that they were of the ‘gymnosperm ‘and not the ‘angiosperm ‘type. The stamens were sometimes elaborately branched, and not so simple as the stamens of the higher plants.

The flowers of Williamsonia were freely exposed on slender branching stems; another group had short stumpy stems, and the numerous flowers were embedded among the leaf-bases. Many examples of the latter type (known as Cycadeoidea) have been found in a petrified state, and their structure and minute anatomy are very fully known. The female cones consisted of seeds borne on long stalks, between which were sterile scales whose ends enlarged beyond the seeds and fitted

closely together, leaving a small opening. The whole was surrounded by protective bracts, and in some species the compound stamens were present in the same flower.

The general arrangement of the parts, as in Williamsonia, thus resembled that of modern flowering plants. The suggestion has therefore been made that the latter were derived from Mesozoic ancestors like Cycadeoidea or Williamsonia— more probably the latter, for it was less specialised, and also rather older. But there are wide differences in detail, even in the flowers, and the other organs do not support the idea of a really close relationship. Just as the seed habit appeared in various groups of plants in the Palaeozoic era, so the flower type of fructification may have been evolved in groups which do not belong to what we now regard as the ‘flowering ‘plants. The analogies between a cycadophyte flower and that of a Magnolia (which many regard as one of the more primitive flowering plants) may be only due to parallel development. These Mesozoic cycadophytes are still a great mystery; early forms belonging to the group are found rarely in the Upper Coal Measures, but we do not know whence they were derived, nor exactly how they are connected with the living cycads.

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