. Fossil plants : for students of botany and geology . Paleobotany. xxxvi] CYCADBOIDEA 407 synaagia in rows. A transverse section just below the ovulate portion of the cone shows a continuous ring of tissue encircling the receptacle with vascular bundles parallel to the surface (fig. 530, A, m); at a higher level the bundles fall into groups preparatory to the breaking up of the disc into separate micro- sporophylls. Immediately above the apex of the central cone the coherent basal portion of the verticil of sporophylls is replaced by the separate rachises which in section have the form of iso
. Fossil plants : for students of botany and geology . Paleobotany. xxxvi] CYCADBOIDEA 407 synaagia in rows. A transverse section just below the ovulate portion of the cone shows a continuous ring of tissue encircling the receptacle with vascular bundles parallel to the surface (fig. 530, A, m); at a higher level the bundles fall into groups preparatory to the breaking up of the disc into separate micro- sporophylls. Immediately above the apex of the central cone the coherent basal portion of the verticil of sporophylls is replaced by the separate rachises which in section have the form of isosceles triangles (fig. 530, B). Each microsporophyll is approximately 10 cm. long; the longest pinnule beiug 1-5 cm. in length and bearing two lateral series of synangia, 10 in each row. At maturity the r ^%'/ 11%'st^. Fig. .531. Cycadeoidea dacotensis. Synangia exposed by weathering and showing the radially disposed loculi. (After Wieland; x 6.) microsporophylls probably spread out and the whole whorl was thrown off leaving an annular rim (fig. 514, d) such as is often seen at the base of older ovulate strobili. The immaturity of the ovules in this (fig. 528) and other specimens led to the suggestion that the strobili of Cycadeoidea were protandrous. The synangia (fig. 531) are several times broader than long and similar in size to those of the Fern Marattia. In each synangium are two rows of elongated locuK (fig. 532) containing oval micro- spores usually with a smooth exine and rather larger than those of recent Cycads. The synangium-waU is composed of a paKsade- layer of thick-walled cells and a layer of smaller and thinner cells: the palisade-layer is narrowest at the apex where dehiscence occurs' and broadest at the base where the hypodermal tissue is more abundant and forms a short thick pedicel. The two rows. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these ill
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Keywords: ., bookcentury1800, bookdecade1890, bookpublishercambr, bookyear1898
