. Fossil plants : for students of botany and geology . Paleobotany. 570 CYCADOPHYTAN FEONDS [CH. Some of the fronds from the Rhaetic of Franconia described by Schenk as N. polymorpha are examples of N. brevis. In N. foly- morpha the distal ends of the segments are blunter, the lamina is much less folded and when folds or corrugations occur they are less regular than in N. brevis. The epidermal cells are polygonal and have thick, straight, walls: oval or circular papillae occur both on the lamina and rachis. The stomata, confined to the lower stirface, are between the veins and each is accompan
. Fossil plants : for students of botany and geology . Paleobotany. 570 CYCADOPHYTAN FEONDS [CH. Some of the fronds from the Rhaetic of Franconia described by Schenk as N. polymorpha are examples of N. brevis. In N. foly- morpha the distal ends of the segments are blunter, the lamina is much less folded and when folds or corrugations occur they are less regular than in N. brevis. The epidermal cells are polygonal and have thick, straight, walls: oval or circular papillae occur both on the lamina and rachis. The stomata, confined to the lower stirface, are between the veins and each is accompanied by a ring of subsidiary cells (cf. fig. 611, B). N. polymorpha is a member of Rhaetic fioras and is recorded also from Liassic rocks at Hori. Nilssonia brevis Brongniart. This species^ (fig. 619, C, D), one of those from Hor on which the genus was founded, has been very fully investigated by Nathorst* whose researches have cleared up many obscure 1^ A, B, Nilssonia brevis; A, section of the frond; B, section of the lamina parallel to the rachis. C, N. saighensis. (A, B, after Nathorst.) The young fronds are circinate like those of Ferns and Cycas. The linear fronds agree generally in habit with those of N. poly- morpha and N. compta, but the lamina is thicker and is characterised by regular transverse corrugations; the veins are very rarely visible except in young leaves which have not reached their full thickness. The fronds may be 50 cm. long and vary in breadth from 1-5 to 12 cm.; the petiole is very short or the frond may be * For other references see Nathorst (09^) p. ' Brongniart (25) p. 218. 3 Nathorst (09^) p. 12, PI. i. figs. 2—, etc. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Seward, A. C. (Albert Charles), 1863-1941. Cambridge : University Press
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