niHHti i mm iHtttt i ' : V \ 1 :Bft B 1 RwmJwflflfi I RKHnKM Rtt RKfiil — I i;: :- i ■ :: ::■■«■.•-■■■■ . ill 111 GEOLOGICAL I URBANA [TE GEOLOGICAL SURVEY 00004 3061 .' A STATE OF ILLINOIS HENRY HORNER, Governor DEPARTMENT OF REGISTRATION AND EDUCATION JOHN J. HALLIHAN. Director DIVISION OF THE STATE GEOLOGICAL SURVEY M. M. LEIGHTON, Chief URBANA CIRCULAR NO. 50 A NEW CYCADOPHYTE AND ITS RELATIVES BY JAMES M. SCHOPF Reprinted From the Transactions, Illinois State Academy of Science, VOL. 31, NO. 2, PP. 107-109, 1939. PRINTED BY AUTHORITY OF THE STATE OF ILLINOIS URBANA, ILLINOIS 1939 (84345) Botany— 1038 Meeting 10 < A New Cycadophyte and its Relatives* James M. Schopf Illinois State Geological Survey, Urbana Recently a new type of Medullosa stem has been discovered in coal balls from the Clarkson Mine, (coal No. 6) at Nashville. This stem may best be compared with the three species of Medullosa which have been described from the English lower Coal Measures. These are Medullosa anglica, M. centrofilis and M. pusilla and the beds from which they are derived are considered roughly equivalent to the Pottsville series of the lower Pennsylvanian of this country. The new stem from Nashville con- sequently is younger geologically than the related European forms. In the accompanying drawings the author has attempted to reconstruct cross sec- tions to scale as the stems would appear if uncrushed or undistorted. All three English species possess three separate main steles. No doubt the English forms are most closely related but their primary structures of determinate growth differ so much in size that they must all be considered valid species. M. centrofilis has a small centrally placed accessory stele which further distinguishes it. A band-like internal periderm layer between the stelar region and the cortex is consistently found in all three English forms. Instead of three steles our new Nashville Medullosa has but two. The stem is somewhat larger than Medullosa anglica as may be noted on the plate since the drawings are approximately on the same scale. The de- current petiole bases are essentially similar although their arrangement on the stem is different. Details of histology also differ showing that this form from Nashville is distinct and not simply a distelar aberration of a typically tristelar species. Perhaps the most noteworthy single feature is the extreme asymmetry of the two steles in this new species. The sec- ondary wood is strongly developed on each vascular member toward the center but only slightly developed on the portion facing the stem exterior. Scott (1) has pointed out that this also occurs in Medullosa anglica and M. pusilla. Examination of De Frame's figures of M. centrofilis show the same condition exists for it too, but in none of these species is the asymmetry of growth so extreme as in the Nashville stem. Whatever the cause for the preponderant secondary growth toward the center of the stem may be, its occurrence in all four of these species indicates that it has some definite significance. A band-like internal periderm layer is present enclosing the stelar tissues of the Nashville Medullosa as in the English stems. Sutcliffia insignis has been suggested by De Fraine as representing a primitive type among the Medullosaroip from wlr'ch the p^iystelnv forms could have been evolved. A reconstruction (more tentative than the other sketches) obtained by combining features illustrated by Scott (2) and by De Fraine (3) is also included on the plate. Sutcliffia also possesses de- current petioles, and a less well defined internal periderm band. There is but a single main vascular cylinder around which are a number of smaller stelar units. These latter structures give rise to the multitudinous small leaf trace bundles and on this account De Fraine regards them more as large foliar traces than as structures homologous with the central stele. It might be inferred that the Nashville Medullosa is derived more directly from a Sutcliffia type of stem than any of the other species on ac-rumt of its fewer steles, notwithstanding that our new form is of some- what younger geologic age than any of the others mentioned. However it Published by permission of the Chief. Illinois State Geological Survey. 108 Illinois State Academy of Science Transactions seems more likely that the reverse is the case since the asymmetry of the steles is probably a specialized feature and this is more extreme in the Nashville stem than in the English Medulloseae. The distelar condition may have come about by elimination of one of the steles of a tristelar form as easily as by the division of the stele of an essentially monostelar plant. The lesser number of steles in the Nashville Medullosa is a feature which serves to distinguish it specifically but this character is less important in itself for judging phylogenetic position. Reduction in complexity of general stelar organization seems more in keeping with features of the histologic organization which will be discussed elsewhere4 in connection with a diagnosis of the new plant. ^^p******^, ftlfaM&w.ifiiifi 10cm Sutchffia msignis Scott Medullosa n.sp. ,8cm , 2cm M. pus il la Scott Medullosa anglica Scott 7cm 5cm M. centrof ilis De Fraine CROSS- SECTIONS OF STEMS OF CERTAIN MEDULLOSACEAE These plants, whose stem structure is so different from those typical of the present are also known to have had fern-like foliage and large nut- like seeds. The male fructification in some instances at least was remark- ably large with tubular sporangia containing male spores which are also much larger and very different from the pollen of modern plants. Even in the case of the best preservations these various organs are habitually found separate from one another. This renders it scientifically impossible to make certain of the specific correlation of seed structure, characters of the male fructification or of the stem or leaf in any single instance which would be comparable with that known for plants living today. We cannot know for certain whether allied stems of different ages with specifically different structure also had different seeds or whether the seed characters were about the same in both cases. The sex organs are considered to be Botany— 1938 Meeting 109 conservative by modern taxonomists so the last possibility might conceiv- ably be of common occurrence in fossil plants. As a consequence of this general situation the identification of the genus Medullosa is based entirely on characters of the stem. Notwithstanding this handicap the leaves, petioles, seeds, male fructifications and roots which go with these stems are sufficiently known, either from isolated cases where the organs are found in actual connection or from their constant association in the same deposits or on the basis of histologic similarities, that their general relationship is apparent. Thus it is known that several Medullosa stems bore foliage which is classified separately as Alethopteris. Structurally preserved petioles de- tached from their stems are designated as Myeloxylon. The characters used in diagnosing species of either of these genera do not necessarily correlate in the course of evolution with species variations exemplified by the stems. Recently fructifications which are related in the Medullosaceae have been discovered. Certain of the Medullosan seeds have been named Ro- todontiospermum and male fructifications are classified under Dolerotheca (in part). It is necessary to use these different names to apply to the various isolated plant organs because their specific inter-correlation cannot be proved with sufficient accuracy. Herein lies the chief difference between the taxonomy of fossil and modern plants. It must be recognized never- theless that these fossils classified under different names have a close natural relationship to the stems previously discussed. In various instances the relationship of assembled organs, as in the case of these mentioned, may be indicated by classifying them together in a more generalized category such as a family. The reconstructions of complete plants of past ages also are based on generalizations of tlrs sort and they have proved a most effective means of summarizing our detailed knowledge of the fossil floras. The foregoing discussion may serve to indicate briefly the problems involved in the paleobotanic study of Medullosaceae. The new stem from Nashville lends emphasis to characters which had previously received little attention. Of course a great deal of study will be necessary before the bo- tanical peculiarities and the relationship of this interesting group of plants become fully known. It is definitely encouraging that additional specimens are being discovered in Illinois coal balls because the European specimens known previously left many pertinent questions unanswered. References 1. Scott, D. H., On Medullosa pusilla : Proc. Roy. Soc. London, B, vol. 87, pp. 222-3, 1913. 2. Scott, D. H., On Sutcliffia insignis, a new type of Medulloseae from the lower coal-measures : Trans. Linn. Soc, London, 2nd. ser., vol. 7, PI. 7, fig. 5, 1906. 3. De Fraine, E., On the structure and affinities of Sutcliffia, in the light of a newly discovered specimen: Ann. Bot., vol. 26. PI. XCI, fig. 1. 1912. 4. Schopf, J. M., Medullosa distelica, a new species of the' Anglica group of Medullosa: Am. Jour. Bot, Vol. 26 (4); 196-207, April, 1939. rWASCHER'S" 31NDJEHS I 507 S. Goodwin I Urbana, III ■ «' IfidlHIilin Jlllii ']•■>•''•:' •,;!',:'>.• Jllli&iififil tfliXHlHUlJ j '•'