A Comparative Study of Stigmarian Appendages and Isoetes Roots
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CSw Su.OO LL, View metadata, citation and similar papers at core.ac.ukbrought to you by CORE provided by Illinois Digital Environment for... STATE OF ILLINOIS DWIGHT H. GREEN, Governor DEPARTMENT OF REGISTRATION AND EDUCATION FRANK G. THOMPSON, Director DIVISION OF THE STATE GEOLOGICAL SURVEY M. M. LEIGHTON, Chief URBANA CIRCULAR NO. 133 A COMPARATIVE STUDY OF STIGMARIAN APPENDAGES AND ISOETES ROOTS WILSON N. STEWAKT iom the American Journal op Botany Vol. 34, June 1947 GEOLOGIC^. ,UIN0\S PRINTED BY AUTHORITY OF THE STATE OF ILLINOIS URBANA, ILLINOIS 1947 'MM'Or.^rATL- GEOLOGICAL SURVfiV 3 3051 00004 6486 ; COMPARATIVE STUDY OF STIGMARIAN APPENDAGES AND ISOETES ROOTS 1 Wilson N. Stewart The roots of Isoetes and the appendages of root system similar to that noted in modern swamp Sfif/maria have been studied in an effort to deter- plants. mine whether the stigmarian appendages are spe- The observations made by Williamson (1886) led cialized leaves borne on a rhizome, as suggested by him to conclude that the stigmarian axes were roots. Solms-Laubach (1891) and recently entertained by Subsequent researches have shown the stigmarian Schoute (1938), or true roots arising from a rhi- axes to have stem-like, not root-like characters. zophore, as concluded by Lang (1923), and Scott Many are similar to those of stems of Lepidoden- (1920). The purpose of this paper is to furnish dron as pointed out by Leclerq (1930), Scott (1920) further anatomical evidence on this controversial and Seward (1910). The aerial steins of Lepido- question which has been discussed by many other dendron in common with the stigmarian axes show: eminent botanists and paleobotanists since the time (1) cambial activity producing a large cylinder of of Williamson's monograph on the morphology and secondary wood composed of scalariform tracheids histology of Stigmaria ficoides (1886). Schoute (2) a well developed middle cortex; (3) a thick (1938) has compiled a resume of the literature con- band of so-called "periderm" on the outside. These cerning this problem. and other features have been incorporated in the Materials and methods.—Coal balls containing diagrammatic drawing of the stigmarian axis shown specimens of Stigmaria were studied from sections in fig. 2. prepared by the nitrocellulose "peel" method, essen- The stigmarian appendages.—The appendages tially the same as given by Graham (1933). The of Stigmaria present features of an anomalous type. specimens studied showed excellent preservation of They project from the axis in a spiral arrangement histological detail. which is similar to a phyllotaxis (fig. 2). With the All of the coal balls are of Pennsylvanian age. exception of their arrangement on the axis, the They were obtained from the collection of the Illi- appendages are very root-like in external appear- nois State Geological Survey" which includes speci- ance. They show a dichotomous branching which is mens assembled by the late Professor A. C. Noe characteristic of the roots of many primitive plants. presence or and by Dr. J. M. Schopf. The absence of root hairs and a root cap does not Living material of Isoetes macrospora was col- appear to have been determined with certainty. Schoute lected from Clear Crooked Lake in Vilas County, (1938) reports that they are absent but the evidence is Wisconsin. Anatomical studies of this species of not clear. There is also some controversy Isoetes were made by the author from preparations as to whether the appendages of Stigmaria were endogenous in origin as are made by the paraffin method. the roots of most plants (Lang, The general characteristics of stigmaria.— 1923), or exogenous, similar to ordinary leaves. There is little proof of Stigmaria is a generic name applying to organs be- the nature of the appendages on the basis of these longing to a group of fossil lycopsid plants. They conventional criteria alone. are dichotomizing root-like axes and appendages of The appendage bundle. The appendage bundle the arboreal lycopods of the Carboniferous period. — lies at a wide angle inclined slightly distal with Lack of notable specialized characters has thus far reference to the main axis as seen in fig. 2. The first prevented a satisfactory classification into groups indication of the beginning of the appendage bundle as small as those designated as genera among is with the outward deflection of a solitary proto- modern plants. xylem element. The protoxylem elements lie be- The dichotomous stigmarian axes as described by tween the pith and the larger metaxylem elements Williamson (1886) may attain a length of slightly at the inner edge of the secondary wood (fig. 2). more than 37 ft. A habit sketch is shown in fig. 1. Thus the arrangement of the primary xylem of the The surface of the axes is generally smooth with main axis is endarch. Other protoxylem elements spirally arranged shallow pits which indicate the and larger metaxylem elements are added adjacent points at which the stigmarian appendages were to the deflected protoxylem element as it traverses attached (fig. 2). The habit of the stigmarian axis the broad vascular ray of the secondary xylem of and appendage system suggests a broad shallow the main axis (fig. 11, 13 and 14). As they pass 1 Received for publication January 7, 1947. 2 through the vascular ray, these primary elements By cooperative agreement. ,lie Coal Division laborato- ries of the Illinois State Geological Survey have been are in turn supplemented by pitted secondary xylem made available for this investigation. Ihe writer wishes elements which are connected with the surrounding :o express his gratitude to Dr. M. M. Leighton, Chief, secondary wood of the main axis (fig. 11, 13 and who made possible the use of these facilities; to Dr. James continuity M. Schopf whose aid was indispensable in the prepara- 14). The between the pitted elements of tion of this paper. the main axis and the pitted elements of the appen- AMERICAN JOURNAL OF BOTANY AN APPENDAGES AND ISOETES ROOTS 317 dage bundle may indicate the origin of secondary "phloem zone." These deposits, shown in fig. 6, are growth in the appendage bundle. interpreted as callus plugs. In the fossil material It has been pointed out by Williamson (1886) they are translucent and distinguishable from cell and Solms-Laubach (1891) that the arrangement walls and cell contents. A cross-section of the same of the xylem in some of the appendage bundles ap- area shows that the end walls of some of these cells pears to be diarch or even triarch, because of the possess a network of bands which may have sepa- presence of more than one group of small xylem rated the numerous sieve fields of a compound sieve elements lying adjacent to the larger metaxylem plate (fig. 5). There is some evidence that sieve elements (fig. 8). Such "protoxylem" apparently areas are also present on the longitudinal walls of was identified in transverse sections on the basis of the phloem cells as well as on the end walls (fig. < size of the elements alone, without regard to the These characters indicate that the cells can be re- type of wall thickenings. Elements of authentic pro- garded as sieve tube elements and may serve as a toxylem have chiefly annular, sometimes spiral histological basis for the identification of the thickenings on their walls, while secondary xylem phloem. elements show characteristic scalariform pitting Cross sections of the appendage bundles as they (fig. 7). From longitudinal serial sections which pass through the secondary cortex of the main axis have been prepared of similar "polyarch" bundles, also show the presence of phloem. The manner in it has been observed that all but one of the groups which the phloem joins the main axis has not been of small xylem elements of a "polyarch" bundle determined, because tissues are poorly preserved have scalariform pitting of their walls characteristic around the periphery of the woody cylinder in the of secondary xylem elements. Only one group of region of the cambium and phloem. small xylem elements has spiral or annular thick- It is of added interest to note that in both cross enings of protoxylem elements. It is evident that and longitudinal sections of the phloem, there ap- the vascular supply of the stigmarian appendage pear within some of the cells ovoid bodies (fig. 5 is monarch as described by Scott (1920) and not a and 6). The shape, the frequency and the relative polyarch arrangement of the xylem elements. size of these bodies within the phloem suggest The small secondary xylem elements of the ap- nuclei. pendage bundle connect with a layer of small sec- The inner cortex.—The inner cortex of the ap- ondary xylem elements at the periphery of the sec- pendage surrounds the vascular bundle (fig. 15), ondary wood of the main axis. This layer has been and judging from the small size of the cells of called the "growth zone" (fig. 12). It can be con- which it is composed, this tissue is not comparable cluded that the small elements of the appendage with the large cells of the secondary cortex of the bundle which are continuous with the cells of the main axis (fig. 21). It seems probable that this "growth zone" do not constitute additional proto- tissue was laid down by the terminal meristem of xylem points. the appendage, as it grew outward through the tis- The "phloem zone."—Adjacent to the xylem of sues of the main axis. The inner cortex maintains the appendage bundle on the side away from the its position about the appendage bundle as it trav- protoxylem, there is a cap of tissue which has been erses the secondary cortex of the main axis (fig.