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AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Art. Till. — A Study of Some American Fossil Cycads* 

 Part VII. — Further JTotes on Disk Structure ; by G. R. 

 Wielaxd. 



A foreword to the present addition to the series of pre- 

 liminary notices on the Cycadeoidea?, which from time to time 

 have been brought out in this Journal, is on the one hand quite 

 as necessary as it is on the other inherently difficult to give. 

 Not since these investigations were begun have any structures 

 been found so baffling to reasonable interpretation as those 

 now brought to light. It is, in the writer's judgment, not 

 enough to simply ascribe these peculiar features of the staini- 

 nate disk as an isolated instance of adaptation. They have to 

 do with bud structures, with reduction from more megaphyl- 

 lous forms, with prefoliation as well as prefloration, and conse- 

 quently lay an emphasis upon the fact that it is at last nec- 

 essary to hypothesize great strobilar variety of form and 

 sexuality in that distant period when the early land plants by 

 means of simple stems and by megaphylly raised their crowns 

 above the soil to make the world's first forests. No difference 

 what interpretation we give these flower buds, exteriorly so 

 like various of the so-called Neuropteris seeds, they constitute 

 evidence that fusion and emplacement of sporophylls coupled 

 with reduction were notable factors in gymnosperm evolution 

 and thus point to an initial hypothesis for the origin of the 

 complex seed coats of early Paleozoic time which no mor- 



* Parts I-III of these studies of American fossil cycads appeared serially 

 in this Journal for March-May, 1899, Part IV in June, 1901, Part V in 

 August, 1911, and Part VI in February, 1912. See also December, 1904 — 

 The Proembryo of the Bennettiteae ; February, 1908 — Historic Fossil Cycads ; 

 December, 1911 — On the Williamsonian Tribe ; September, 1913 — The Liassic 

 Flora of the Mixteca Alta of Mexico, its Composition, Age, and Source. 



Am. Jour. Sci.— Fourth Series, Vol. XXXVIII, No. 224.— August, 1914. 

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