. Heredity and evolution in plants . S36fl«.. FIG. 92.—To the left, Cacadeoidea dacotensis Macbride. Longitudinalsection of a silicified specimen of a bisporangiate cone (unexpanded flower),so taken that the pinnules of the microsporophylls on both sides of thecentral axis, or receptacle, are successively cut throughout their entirelength. The lines indicate the planes of various sections through the cone,published in Wielands American Fossil Cycads. To the right Cycado-cephalus Sewardi Nathorst. Microsporangiate cone, natural size, preservedas an impression on a flat slab. From a fossil-beari
. Heredity and evolution in plants . S36fl«.. FIG. 92.—To the left, Cacadeoidea dacotensis Macbride. Longitudinalsection of a silicified specimen of a bisporangiate cone (unexpanded flower),so taken that the pinnules of the microsporophylls on both sides of thecentral axis, or receptacle, are successively cut throughout their entirelength. The lines indicate the planes of various sections through the cone,published in Wielands American Fossil Cycads. To the right Cycado-cephalus Sewardi Nathorst. Microsporangiate cone, natural size, preservedas an impression on a flat slab. From a fossil-bearing bed of the Trias, atBjuf, Southern Sweden. (Left figure from Wieland, right figure fromNathorst.) closely a plant may resemble both a cycadophyte and a a sense this plant may be called a living fossil. Speci-mens have since come into flower in botanic gardens, andthe typical cycadaceous cones (Fig. 91) leave no doubtthat the plant is a true cycadophyte. THE EVOLUTION OP PLANTS 2OQ 142. Derivation of New —Attention shoul
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Keywords: ., bookcentury1900, bookdecade1920, bookidheredityevol, bookyear1920
