Observations on Petiolar Branching and Foliage of an American Botryopteris

Coal-ball material from the Berryville collecting locality of the McLeansboro group in southeastern Illinois has shown the exact method of branching of the petiole trace which has been followed with close serial sections. The specimens were complete enough to discredit the hypothetical method of branching postulated by Bertrand and to substantiate the type suggested by Graham on the basis of a single cross-section. Although the suggestion of the possession of leaves by certain members of the genus has been reported (Renault, 1896; Kraentzel, 1934; Darrah, 1941), the general consensus of opinion was that no laminations of any kind are borne on the lateral appendages (Andrews, 1951). The structure of the plants is thought to represent a primitive condition transitional between a psilophytic branching system and a true fern -frond. With the present discovery of fern-like, pinnute-bearing pinnae assignable to Botryopteris, it is suggested that although the genus is a relatively primitive one, it may occupy a somewhat more advanced phyletic position than was previously assigned to it. Description of petiolar axes.-As in B. forensis, the petioles of our specimens possess an w-shaped strand of metaxylem, with protoxylem situated at the tips and to some extent around the outer flanks of the two lateral arms (fig. 1). Protoxylem elemenits are annular, spiral, and scalariform, while metaxylem tracheids possess multiseriate circular bordered pits (fig. 2). The innermost cortex surrounding the traces is lost in all the specimens, its extent being indicated only by a completely unpreserved zone about the strand. Immediately surrounding this cavity in larger axes is a thin band of scierenchyma. Outside the sclerenchyma are two zones of the cortex, the inner zone of which is composed of relatively laege, thin-walled cells in contrast to, the denser outer zone. From the epidermis arise long, unbranched, multicellular hairs (figs. 1, 3). The largest of the petioles average 6 mm in diameter, with progressively smaller dimensions for axes of secondary, tertiary, and even higher degrees of pinnation. 374