Vascular Construction and Development in the Aerial Stem of Prionium (Juncaceae) Author(s): Martin H. Zimmermann and P. B. Tomlinson Source: American Journal of Botany, Vol. 55, No. 9 (Oct., 1968), pp. 1100-1109 Published by: Botanical Society of America Stable URL: http://www.jstor.org/stable/2440478 . Accessed: 19/08/2011 13:58 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. Botanical Society of America is collaborating with JSTOR to digitize, preserve and extend access to American Journal of Botany. http://www.jstor.org Amer.J. Bot. 55(9): 1100-1109.1968. VASCULAR CONSTRUCTION AND DEVELIOPMENT IN THE AERIAL STEM OF PRIONIUM (JUNCACEAE)1 MARTIN H. ZIMMERMANN AND P. B. TOMLINSON HarvardUniversity, Cabot Foundation,Petersham, Massachusetts and FairchildTropical Garden, Miami, Florida A B S T R A C T The aerial stemof Prioniumhas been studiedby motion-pictureanalysis which permits the reliabletracing of one amonghundreds of vascularstrands throughout long series of transverse sections.By plottingthe path of many bundles in the maturestem, a quantitative,3-dimensional analysisof their distribution has beenmade, and by repeatingthis in theapical regionan under- standingof vasculardevelopment has been achieved.In the maturestem axial continuityis maintainedby a verticalbundle which branches from each leaf tracejust beforethis enters the leaf base. Lateral continuityresults from bridges which link leaf traceswith nearbyvertical bundles.Development of the provascularsystem involves a meristematiccap into whichthe blindends of verticalbundles can be followed.Leaf tracesare prodlucedcontinuously in associa- tionwith developing leaf primordia for a periodof over30 plastochrones;they connect with the verticalbundles in the meristematiccap and so establishthe essentialvascular configuration whichis laterreorientated through about 900 by overallgrowth of the crown. The last bundlesto differentiatefrom the leaf do so outsidethe meristematic cap and thusfail to makecontact with the axial system;they appear in the matureaxis as blind-endingcortical bundles. Prionium is only distantlyrelated to palms and its vascularhistology is quite different.Nevertheless, the courseof vascularbundles and the originof thispattern in the stemresembles that of a palm. It is suggestedthat we are examiningthe fundamental pattern of vascular development in large monocotyledons. RECENT reexaminationof the vascular system in relevatnceto the situation as it exists in nature the stems of largermonocotyledons, particularly (Tomlinson and Zimmermann,1966). Neverthe- the palms, shows that earlier anatomists had less, since the time of von Mohl, the "palm- incompletelyobserved the fundamentalprinciple type" of vascular arrangementhas been regarded underlyingconstruction of these axes and could as the one basic for the stem in most groups of thereforearrive at no true understandingof monocotyledons.Continuing reexaminationof developmentalprocesses (Zimmermann and Tom- monocotyledonousanatomy, far from demolishing linson,1965, 1967). Using the small palm Rhapis this concept,is likelyto strengthenit by putting excelsa as a model it has been shown that the it on a firm factual foundation which was classical researches of Hugo von Mohl (1824, originallylacking. The only literatureto which 1849) and de Mirbel (1843-44) on the palm stem modernwork has any directrelevance is that of were correctbut incomplete.They did not reveal about 100 years ago because in subsequentyears the axial continuityof vascular strandsalthough anatomistshave virtuallyneglected a topicwhich, this is essentialto an appreciationof the pathway like many others in the classical botanical forlong-distance transport. It has also been shown tradition,has been regardedas "fullyworked out" that any understandingof this pathway which and thereforedismissed by later generationsof modern textbooks may claim to illustrate has investigators. arisen by a processof "paper evolution" with no Investigationof the palm Rhapis revealed a well-definedorganization of the maturevascular 1 Receivedfor publication 30 April1968. system,as well as a clearlyrecognizable pattern Researchof one of theauthors (P.B.T.) on theanatomy of development. The question naturally arose of monocotyledonsis supportedby N.S.F. Grant GB- 5762-X. whetherthis vascular patternis fundamentalfor the palms and perhaps even forthe monocotyle- The writersexpress their appreciation to Dr. D. F. dons as a whole.The answerto this questionwill Cutlerof the Royal BotanicGardens, Kew, England,and Dr. R. G. Streyof the Natal Herbarium,Durban, South requirea great deal of work.A numberof plants Africa,for the materialon which the investigationis in various familieshave been observed but any based, and to Miss AnneBellenger and GeorgeBailey for vascular pattern fundamentallydifferent from preparationof sections.They thankProfessor Ralph H. Wetmorefor his criticalreview of the manuscriptand for that of Rhapis has not been found.The present manyvaluable discussions. articleprovides further evidence in this direction 1100 October,1968] ZIMMERMANN AND TOMLINSON STEM OF PRIONIUMt 1101 by demonstratingthat the vascular pattern, subsequently only every third section was whichseems characteristicof the palm stem,also kept to give a total of 200 slides. occurs in a plant having no obvious systematic Sectionswere bleached briefly in Clorox,washed affinitywith the palms. The presentstudy of the well in runningwater and stainedin safraninand "tree-rush," Prionium serr-atum(Juncaceae), Delafield's haematoxylin. They were then amply confirmsour prediction.This species was mountedone per slide to permitvascular analysis selected because it was a suitably large mono- by meansof our opticalshuttle (Zimmermann and cotyledonand yet proved amenable to investiga- Tomlinson, 1966). For a study of histological tion by the methods we have employed. The details thinner sections were cut from small anatomy of Prionium has been described in blocks which had been embedded in celloidin. considerable detail by Buchenau (1893) but These sections were stained either in safranin without attention to the arrangement and and Delafield's haematoxylinor in the tannic developmentof the vascular bundles. acid-ferricchloride-resorcin blue combinationof Cheadle, Gifford,and Esau (1953). MATERIAL AND METHODS-Material-Prionium Shoot apices wveredehydrated and embedded serratum(L.f.) Drege is a gregariousplant of wet in Paraplast by normal procedures.Continuous places in the Cape and elsewherein South Africa series of sections 10,u thick, in transverseand whereit is knownas "Palmiet." Livingspecimens longitudinalplanes, were cut on a rotarymicro- have not been seen but Hooker (1868) illustrated tome, stained in safraninand Delafield's haema- cultivated specimens and fromhis figuressub- toxylinand mountedin the usual way. Individual sequent habit drawingsare largelyderived (e.g., transversesections were so large that only two Buchenau, 1893, 1906; Vierhapper,1930). It is could be mounted on each 50 X 75-mm micro- describedby Buchenau as a plant withperennial scope slide. This proved beneficialin the sub- erect shoots arisingfrom creeping, scale-bearing sequent plotting of the developing vascular rhizomes. The aerial stems considered in this systemsince the optical shuttlecould be used in study are erect shoots up to 2 m tall with a the way describedbelow. terminalcluster of lanceolate leaves up to 1 m long,each shoot eventuallyproducing a terminal, Serial analysis-The vascular system of the paniculate inflorescence.Stems are clothed with adult axis was unravelled with the aid of the the fibrousremains of persistentleaf bases, the cinematographicmethods, including the optical axis proper being of the order of 5 cm in diam. shuttle, described in detail elsewhere(Zimmer- Internodesare close set and only 2-3 mm long. mann and Tomlinson,1965, 1966). This involves Branching of the erect axis is infrequent,but the use of a cine camera to photograph,frame by accordingto Buchenau(1893) it may sometimesbe frame,successive sectionsobserved throughthe sympodial and associated with flowering,as in microscope.The optical shuttleis a device which Yucca and many other arborescentmonocotyle- uses two microscopesto superimposethe images dons. Otherwise branching is irregular and fromtwo successivesections in such a way that determinedby no obvious morphologicalrule. they are preciselyregistered in the filmplane of Axillary buds, protected by a conspicuous the camera and then photographedin turn. A prophyll,are distributedwithout obvious order furtherimprovement of the method described and are stronglysuppressed. in the earlier article is a foot-operateddevice A portion of the aerial stem togetherwith a whichswitches each microscopeon or offin turn, numberof shoot apices fixedin FAA were pro- leaving both hands freeto adjust the microscope vided by Dr. R. G. Streyof the Natal Herbarium, stage. Optical alignmentof subsequent sections Durban, South Africa.The axis whichwe studied was then achieved by reductionof the apparent was mature but only slightly hardened and motionbetween