. Morphology of gymnosperms. Gymnosperms; Plant morphology. PC b Fig. 47.—Trigonocarpum Parkinsonii: diagrammatic transverse section through the micropyle at about the level of pcb in fig. 46; for lettering see fig. 48. tions may occur in the nucellar tracheal mantle, which may be re- placed by a vascular network or by distinct vascular strands. Later, Scott and Maslen (73) described two species of Trigono- carpum {T. Parkin- sonii was probably the seed of Medul- losa anglica) from the Coal-measures (figs. 46-48) which conform fully to the Stephanos permum type of structure, in these cases the
. Morphology of gymnosperms. Gymnosperms; Plant morphology. PC b Fig. 47.—Trigonocarpum Parkinsonii: diagrammatic transverse section through the micropyle at about the level of pcb in fig. 46; for lettering see fig. 48. tions may occur in the nucellar tracheal mantle, which may be re- placed by a vascular network or by distinct vascular strands. Later, Scott and Maslen (73) described two species of Trigono- carpum {T. Parkin- sonii was probably the seed of Medul- losa anglica) from the Coal-measures (figs. 46-48) which conform fully to the Stephanos permum type of structure, in these cases the three layers of the testa being distin- guished, and the vascular strands oc- curring in two sets (an outer system in the outer fleshy layer, and an inner system traversing the periphery of the free nucellus), both distinctly cycadean characters. The inner vascular sys- tem forms a " prac- tically continuous sheath" in the lower part of the nucellus, and is traceable through the whole length of the nucellus, almost to the base of the pollen chamber. A remarkable feature of these winged seeds is the conspicuous micropylar. m m Fig. 48.—Trigonocarpum Parkinsonii: diagrammatic trans- verse section at about the level of mm in fig. 46; lettering for figs. 46-48: sa, sarcotesta; I, its limiting layers; sc, sclerotesta; mi, micropyle; it, remains of "inner flesh''; sab, sarcotestal bundles; pc, pollen chamber; pcb, its beak; s, septum at bottom of pollen chamber; ne, nucellar epidermis; nt, nucellar tracheal system; mm, megaspore membrane; td, tracheal disk at chalaza; chb, chalazal bundle; >•' and r', principal and secondary ridges; all Xabout 3.—^Maslen in Scotx (87).. 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 Coulter, John Merle, 1851-1928; Chamberlain, Charles Joseph, b. 1863; C
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