. Heredity and evolution in plants . rganizedas those of to-day, are found far back in the earliest fossil-bearing strata of the Paleozoic. Great forest types ex-isted as early as the Devonian. Later in the Carboniferousoccur many seed-bearing ferns. These have been calledCycadofilicales (cycadaceous ferns), or, by some, Pterido-sperms. Recent studies have disclosed the fact thatmost of the fossil plants from the Carboniferous coal-bearing strata, formerly thought to be ferns, are not evencryptogams, but are these fern-like seed-bearing best known pteridosperm is Lyginodendron oldha
. Heredity and evolution in plants . rganizedas those of to-day, are found far back in the earliest fossil-bearing strata of the Paleozoic. Great forest types ex-isted as early as the Devonian. Later in the Carboniferousoccur many seed-bearing ferns. These have been calledCycadofilicales (cycadaceous ferns), or, by some, Pterido-sperms. Recent studies have disclosed the fact thatmost of the fossil plants from the Carboniferous coal-bearing strata, formerly thought to be ferns, are not evencryptogams, but are these fern-like seed-bearing best known pteridosperm is Lyginodendron oldhamium(Fig. 86), first described from fossil leaves, in 1829, asa tree-fern, under the name Sphenopteris investigations extending over nearly 90 years, we are 2OI 2O2 IIKRKDITV AM) KM HI IU>\ i\ PLANTS now in position to draw a fairly complete picture of theplant as it must have appeared when living. It was in effect a little tree-fern, with long, slender,sometimes branched, stem, 4 centimeters or less in diarm--. FIG. 86.—Lyginodcndron oldliamium. Pinna of a microsporophyll,found in an ironstone nodule. Before its identity \vas established thisspecimen was named Cntssollicia llocninghansi. The somewhat peltatefertile pinules on the ultimate branches, bear each a fringe of micro-sporangia about 3 mm. long. The appearance has been likened to thatof a fringed epaulet. (After Scott, from a photo by Kidston.) ter, and provided with spines by means of which it prob-ably climbed on its neighbors. The foliage was disposedspirally and consisted of relatively very large, finelydivided fronds with small, thick pinnules with revolute THE EVOLUTION OF PLANTS 203 margins, suggesting a xerophytic or halophytic stem in the lower portion gave rise to numbers ofslender roots, some of which appear to have been aerialin their origin. These grew downward and often branchedwhere they entered the soil.
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Keywords: ., bookcentury1900, bookdecade1920, bookidheredityevol, bookyear1920
