American Fossil Cycads, Vol. 2: Taxonomy (Classic Reprint)

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9781330265758: American Fossil Cycads, Vol. 2: Taxonomy (Classic Reprint)

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G R Wieland
Edité par Forgotten Books, United States (2015)
ISBN 10 : 1330265750 ISBN 13 : 9781330265758
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Description du livre Forgotten Books, United States, 2015. Paperback. État : New. 226 x 150 mm. Language: English . Brand New Book ***** Print on Demand *****.Excerpt from American Fossil Cycads, Vol. 2: Taxonomy In brinsring to completion a second volume on the petrified cycads the material inviting exact study seems more impressive than ever. The actual number of stems in the several collections has not been much increased since the publication of Volume I, but the aggregate of finely conserved structure which is gradually being located and made available for study is great. Nordo the European collections fall behind those of America in interest. Although somewhat less extensive, their structural interest coequals that of the American collections. Easily the most noteworthy addition to the American series is the monocarpic trunk of the United States National Museum discovered by Dr. N. H. Darton in the Hermosa segment of the Black Hills Rim in certain respects the most remarkable fossil plant of any kind or age ever recovered. Fortunately, however, the study of the Cycadeoids has reached a point where progress is less dependent on rare or unusually conserved specimens. To this result the discovery of related Williamsonians has greatly contributed; equally so the precise methods for the study of casts and imprints introduced by Professor Nathorst and others. The expanding field of cycad investigation has thus taken on permanent interest, and it is certain that museum collections will be signally enlarged, while those already accumulated hold the attention of botanists. In the prefatory note to Volume I the opportunity for extended study and comparison of Cycadeoidean seeds was emphasized, and it is believed that the chapter now devoted to this subject fully justifies singling it out. Even without the increase of material afforded by the Hermosa cycadeoid it was evident that the seeds held far greater interest than the space earlier devoted to them indicated. At the present time, amongst subjects near at hand, the simpler one of stem structure may be noted. The anatomy of the fossil gymnosperms has long been an unsatisfactory subject because of the great size or fragmentary character of the Mesozoic stems. The wedge of a Cycadcoidca trunk is comparable to the wedge of even the tallest conifer. It affords complete structural details within restricted limits and later studies will reveal the type of change which may be expected in gymnospermous stems in passing from pith to cortex and from base to apex. The unexpected discovery of the homed disks of Cycadeoidea colossalis has led to comparisons with seed-coats suggesting some kind of ancient and far-reaching homology between megaspore and floral envelopes. The ideas advanced are not theories; they are hypothetic. If any of these conceptions should later receive confirmation or proof their importance in evolutionary theory must be very great. For this reason the discussions of the closing chapters take on a speculative form. No claim of triumphant demonstration is made or under the circumstances can be made. Refutation there may well be. But in either instance it is with confidence that the group origins are held to be more nearly discrete than may be implied from most discussions of the theory of descent. It has been found necessary to lay increasing stress on the need for adhering to the nomenclature of convenience already established for the silicified stems. This is indispensable to progress in the taxonomy, and to a certain extent in general structure. These stems are unique, and must be recognized as difficult to catalogue. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at. N° de réf. du libraire AAV9781330265758

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2.

G R Wieland
Edité par Forgotten Books, United States (2015)
ISBN 10 : 1330265750 ISBN 13 : 9781330265758
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Description du livre Forgotten Books, United States, 2015. Paperback. État : New. 226 x 150 mm. Language: English . Brand New Book ***** Print on Demand *****. Excerpt from American Fossil Cycads, Vol. 2: Taxonomy In brinsring to completion a second volume on the petrified cycads the material inviting exact study seems more impressive than ever. The actual number of stems in the several collections has not been much increased since the publication of Volume I, but the aggregate of finely conserved structure which is gradually being located and made available for study is great. Nordo the European collections fall behind those of America in interest. Although somewhat less extensive, their structural interest coequals that of the American collections. Easily the most noteworthy addition to the American series is the monocarpic trunk of the United States National Museum discovered by Dr. N. H. Darton in the Hermosa segment of the Black Hills Rim in certain respects the most remarkable fossil plant of any kind or age ever recovered. Fortunately, however, the study of the Cycadeoids has reached a point where progress is less dependent on rare or unusually conserved specimens. To this result the discovery of related Williamsonians has greatly contributed; equally so the precise methods for the study of casts and imprints introduced by Professor Nathorst and others. The expanding field of cycad investigation has thus taken on permanent interest, and it is certain that museum collections will be signally enlarged, while those already accumulated hold the attention of botanists. In the prefatory note to Volume I the opportunity for extended study and comparison of Cycadeoidean seeds was emphasized, and it is believed that the chapter now devoted to this subject fully justifies singling it out. Even without the increase of material afforded by the Hermosa cycadeoid it was evident that the seeds held far greater interest than the space earlier devoted to them indicated. At the present time, amongst subjects near at hand, the simpler one of stem structure may be noted. The anatomy of the fossil gymnosperms has long been an unsatisfactory subject because of the great size or fragmentary character of the Mesozoic stems. The wedge of a Cycadcoidca trunk is comparable to the wedge of even the tallest conifer. It affords complete structural details within restricted limits and later studies will reveal the type of change which may be expected in gymnospermous stems in passing from pith to cortex and from base to apex. The unexpected discovery of the homed disks of Cycadeoidea colossalis has led to comparisons with seed-coats suggesting some kind of ancient and far-reaching homology between megaspore and floral envelopes. The ideas advanced are not theories; they are hypothetic. If any of these conceptions should later receive confirmation or proof their importance in evolutionary theory must be very great. For this reason the discussions of the closing chapters take on a speculative form. No claim of triumphant demonstration is made or under the circumstances can be made. Refutation there may well be. But in either instance it is with confidence that the group origins are held to be more nearly discrete than may be implied from most discussions of the theory of descent. It has been found necessary to lay increasing stress on the need for adhering to the nomenclature of convenience already established for the silicified stems. This is indispensable to progress in the taxonomy, and to a certain extent in general structure. These stems are unique, and must be recognized as difficult to catalogue. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at. N° de réf. du libraire AAV9781330265758

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G R Wieland
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Description du livre Forgotten Books, 2015. PAP. État : New. New Book. Delivered from our UK warehouse in 3 to 5 business days. THIS BOOK IS PRINTED ON DEMAND. Established seller since 2000. N° de réf. du libraire IQ-9781330265758

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G R Wieland
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G. R. Wieland
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Description du livre Forgotten Books, 2015. Paperback. État : New. book. N° de réf. du libraire 1330265750

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Wieland, G. R.
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