. The classification of flowering plants. Plants. Ill] GNETACEAE 125 terminate in rounded three-chambered anthers, dehiscing across the top (fig. 49, D). The pollen-grains are elliptical. In the centre of" the flower is an erect sterile ovule, the integument of which expands above into a broad stigma-like plate (fig. 49, E).. Fig. 49. Tumhoa (Welwitschia). A. Plant bearing female inflorescences (much reduced). B. Eipe female cone, ^ nat. size. C. Staminate flower, one of the inner perianth-leaves is drawn back, exposing the monadelphous stamens, enlarged. D. Upper part of a stamen and ant
. The classification of flowering plants. Plants. Ill] GNETACEAE 125 terminate in rounded three-chambered anthers, dehiscing across the top (fig. 49, D). The pollen-grains are elliptical. In the centre of" the flower is an erect sterile ovule, the integument of which expands above into a broad stigma-like plate (fig. 49, E).. Fig. 49. Tumhoa (Welwitschia). A. Plant bearing female inflorescences (much reduced). B. Eipe female cone, ^ nat. size. C. Staminate flower, one of the inner perianth-leaves is drawn back, exposing the monadelphous stamens, enlarged. D. Upper part of a stamen and anther, enlarged. E. Sterile ovule from staminate flower, enlarged. F. Diagram of staminate flower with its subtending bract. G. Seed, shewing wing-like expansions of perianth and the projecting micropjle, x^. H. The same in transverse section, x ^. (A—F, from Sir J. Hooker's original paper; G, H, from dried specimens collected by Dr Welwitsch.) I. Preparation from a germinating seed shewing the hypocotyledonarv sucker h, which remains in the seed, the radicle having grown downwards and the cotyledons having been carried up on the hypocotyl; s, suspensor still attached to the remains of the perisperm. After Bower. The sac-like perianth of the female flower is laterally com- pressed by the cone-scales into the form of a pair of Avings. It is homologous with the outer whorl in the male flower, and originates from two lateral primordia, which subsequently become united. There is no trace of male organs. The integument of the ovule is drawn out into a long narrow neck, which overtops the perianth and is notched at the apex. The sporogenous cells, as in other Gymnosperms, become buried beneath nucellar tissue, which forms a somewhat per- sistent cap, recalling the similar structure in Cycads and Ginkgo, but there is no evidence that a pollen-chamber is formed. The details of development of the functional mega- spore have not been worked out, but the tissue at the. Please note that th
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectplants, bookyear1904
