II. On the Structure of Zygopteris primaria (Cotta) and on the Relations between the genera Zygopteris, Etapteris and Botrychioxvlon

Just a hundred years ago Bernhard von Cotta described, in one of the earliest works dealing with the internal structure of silicified plants, the Permian tree-fern now known as Zygopteris primaria. The general belief is that only one specimen was ever discovered ; our knowledge of the structure is thus confined to the petiole, and that, too, as we shall see, is defective. It was therefore a pleasant surprise when, during a visit to Berlin in September, 1929, I came across a magnificent specimen with the centre occupied by a fairly well-preserved protostelic stem.