| Abstract: | Phloem histology in the petioles of two genera of Pennsylvanian ferns is detailed from coal balls collected at various localities in North America. Both Ankyropteris and Anachoropteris have primary phloem that completely surrounds the central xylem trace and is separated from it by a parenchymatous sheath. Ankyropteris contains very narrow (about 13.5 μm diam) sieve elements and a few strands of phloem parenchyma. End walls are either horizontal or slightly oblique and sieve areas as well as scattered individual pores have been observed. Anachoropteris phloem contains two different sizes of sieve elements. Small sieve elements that surround the C-shaped trace are similar to those seen in Ankyropteris. Larger elements (approximately 50–120 μm in diam) are present only within the C-shaped trace, and are elongate (up to 2.5 mm) with very oblique end walls. Sieve areas on these large cells are conspicuous, 5–8.5 μm in diam and aggregated into groups. The cell wall within each sieve area appears to be composed of criss-crossed fibrillar material. Phloem anatomy in these two ferns is compared to that previously described in other Carboniferous vascular cryptogams, as well as that known from extant plants. |
