IAWA Journal, Vol. 19 (3),1998: 279-283 INTRUSIVE CAVITIES IN EUPHORBIACEAE FIBRE WALLS by Claudia Luizon Dias-Lerne & Veronica Angyalossy-Alfonso Botany Department, Biosciences Institute, Silo Paulo University, c.P. 11461, 05422-970, Silo Paulo-SP, Brazil SUMMARY Fibres with intrusive cavities were present in Alchornea sidifolia, Al­ chornea triplinervia, Croton floribundus, Sapium glandulatum, and Sebastiania serrata (Euphorbiaceae). These cavities are the result of an intrusive growth of fibres which detour when they encounter a cellular obstacle, form either a fork or a concavity around the obstacle, and sub­ sequently unite. The term 'intrusive cavity' is proposed for this struc­ ture. Key words: Intrusive cavity, fibre cavities, Euphorbiaceae, Alchornea, Croton, Sapium, Sebastiania. INTRODUCTION Xylem cavity elements were described for the first time by Gomes et al. (1988) in tracheids of Araucaria angustifolia and in fibre and axial parenchyma cells of Cabralea glaberrima. They called these elements, respectively, 'transpierced tracheids', 'transpierced fibres', and 'transpierced axial contact-parenchyma cells', and, accord­ ing to them, the presence of such cavities could possibly be formed either through the dissolution of the central core of a wide plant-like trabecula, or through the concur­ rent development of matching lateral piercing protuberances of two neighboring tracheids. Similar cavities also have been mentioned by Luchi and Mazzoni-Viveiros (1988), Luchi (1990), and Zhong et al. (1992). The Euphorbiaceae is one of the families in which fibre cavities have been ob­ served. This study provides additional information on the formation of the cavities in some species of the Euphorbiaceae. MATERIAL AND METHODS The following plant material was collected at the University of Säo Paulo's forest (Säo Paulo, Brazil): Alchornea sidifolia Muell. Arg.: SPFw 424,425; Alchornea tri­ plinervia (Spreng.) Muell. Arg.: SPFw 426, 427; Crotonfloribundus Spreng.: SPFw 428,429; Sapium glandulatum (Vell.) Pax: SPFw 430; and Sebastiania serrata (Baill.) Muell. Arg.: SPFw 431, 432. Stern and root segments of living adult trees (over three meters height) identified by MSc Lucia Rossi (Botanic Institute of Säo Paulo, Brazil) were taken for this study Downloaded from Brill.com09/28/2021 12:59:18PM via free access 280 IAWA Journal, Vol. 19 (3), 1998 (vouchers are in that research center). Wood sampIes were deposited at the University of Silo Paulo, Biosciences Institute's wood collection, Silo Paulo, Brazil (SPFw). Stern sampIes were collected at breast height (1.30 m) and root samples at a depth 30 cm below the soil surface and 30-50 cm from the central axis of the tree. Blocks of approximately 1 cm3 were taken from root and stern sampIes and soften­ ed by boiling in water and glycerin. Longitudinal tangential and radial sections (15- 20 flm wide) were cut with a microtome. Afterwards the sections were stained in safranin and/or safranin and hematoxylin, and mounted using synthetic resin on per- Fig. 1. Croton floribundus. Stern. Tangential section. Fibre with cavity (C). - Fig. 2 & 3. Stern. Tangential seetion. Forked fibre with ray obstacle-cell (arrow). - 2: Crotonfloribundus. - 3: Alchonea triplinervia. Downloaded from Brill.com09/28/2021 12:59:18PM via free access Dias-Lerne & Angyalossy-Alfonso - Intrusive cavities in fibre walls 281 manent slides (Dias-Lerne 1994). Wood was macerated using Franklin' s method modi­ fied by Berlyn and Miksche (1976). Over 200 semi-permanent slides were prepared. RESULTS Fibre cavities occur in the middle as weIl at the end of cells (Fig. 1, 7-11) and they were observed in roots and sterns of all species analysed. Fibre cavities were common in Croton floribundus so this species was chosen for a more detailed analysis of (le different stages in the formation of the cavities. Fibres grow by intrusive growth. When an obstacle, like a ray cell, is encountered, the fibres keep on growing by forking (Fig. 2-5) or sometimes form concavities (Fig. 7-9, arrow) at the place of contact with the ray cello Figure 5 shows that the cavity is the result of the detour of the fibre around two ray cells. The two fibre branches continue growing side by side without fusion (Fig. 9, 10, *). It seems that fusion later takes place between the branches, probably by cell wall dissolution, giving rise to the cavity (Fig. 9-11 ,C). In reference to the formation of concavities (Fig. 7-9, arrow), it seems that the cavities are formed by an unequal growth of one of the fibre branches (Fig. 7, 8, arrow). Figure 6 (arrow) shows a probable cavity; however, there are two superim­ posed fibres suggesting a cavity. After separation of these two cells (Fig. 7), it was found that there actually was only a concavity in one cell (Fig. 7, arrow) and its mold in the other one (Fig. 7, *). Sometimes different stages in cavity formation were observed in the same fibre (Fig. 9, 10). DISCUSSION The term 'transpierced region' used by Gomes et al. (1988) for the cavities observ­ ed in tracheids, fibres and axial parenchyma has also been accepted by other authors. Luchi and Mazzoni-Viveiros (1988) and Luchi (1990) observed cavities in fibres and/or axial parenchyma cells of Alchornea triplinervia, Aegiphila sellowiana, Tibouchina candolleana, Vochysia tucanorum, and Tapirira marchandii. Although these authors noted that forked fibres tended to reunite at their tips, they accepted the 'transpierced' term as proposed by Gomes et al. (1988). Zhong et al. (1992) mentioned the same situation in some species of Ulmaceae, calling these cavities 'simple perforations'. They agreed with Gomes et al. (1988), as regards their formation, stating that these perforations are probably the result of trans­ piercing tip growth of adjoining fibres. After observing the different formation stages ofthe cavities, it appears that a fibre forks upon encountering an obstacle, such as a ray cello The fibre continues to grow and the forks subsequently fuse; this suggests that the transpiercing of one cell by an­ other one does not occur, as described by Gomes et al. (1988), and accepted by Luchi and Mazzoni-Viveiros (1988), Luchi (1990), and Zhong et al. (1992). Downloaded from Brill.com09/28/2021 12:59:18PM via free access 282 IAWA Journal, Vol. 19 (3),1998 100v.m Olllll I 1111 "OlUI 9 8 10 Downloaded from Brill.com09/28/2021 12:59:18PM via free access Dias-Lerne & Angyalossy-Alfonso - Intrusive cavities in fibre walls 283 The cavities make no communication with other cells, and represent aspace that was occupied by the obstacle-cell and are limited by a secondary wall. Because of this, we do not agree with the term 'simple perforation', used by Zhong et al. (1992), because the cavity does not arise in the same way as a perforation plate. Dur observa­ tions indicate the cavity is formed by cell intrusive growth, and so we propose the term 'intrusive cavity' for this condition. We suggest that histochemical and ultrastructural studies be done to clarify the fusion process of the fibre branches during the intrusive cavity formation. ACKNOWLEDGEMENTS This study was supported by FAPESP - Funda~ilo de Amparo a Pesquisa do Estado de Silo Paulo. We would like to thank Mr. Antonio Carlos Barbosa for his help with the sections. REFERENCES Berlyn, G.P. & lP. Miksche. 1976. Botanical microtechnique and cytochemistry. Ed. Iowa State University Press, Iowa. Dias-Lerne, C.L. 1994. Anatomia comparada do lenho do caule, raiz e ramo de algumas espe­ cies de Euphorbiaceae da MataAtliintica. Disserta~ilo de Mestrado. Instituto de Biociencias, Universidade de Silo Paulo, Silo Paulo, Brazil. Gomes, A v., L. L. Teixeira, G. B. Muniz & A Bohren. 1988. Transpierced tracheids, trabeculae and other unusual features in Gymnosperm wood. Conferencia Global da Divisilo 5 - Produtos Florestais. International Union of Forestry Research Organizations IUFRO. Luchi, AE. 1990. Estudo anatömico do lenho em especies de mata ciliar da Serra do Cip6 (MG). Disserta~ilo de Mestrado. Instituto de Biociencias. Universidade de Silo Paulo, Silo Paulo, Brazil. Luchi, A E. & S. C. Mazzoni-Viveiros. 1988. Regiöes de transpasse em e1ementos celulares de lenho de A1chornea triplinervia (Spreng.) Mue1l. Arg. (Euphorbiaceae). Resumo do Congresso da Sociedade de Botänica de Silo Paul0, 7, Rio Claro, Silo Paul0, Brazil. Zhong, Y., P. Baas & E.A Wheeler. 1992. Wood anatomy oftrees and shrubs from China. IV. Ulmaceae. IAWA Bull. n.s. 13: 419-453. Fig. 4-11. Croton floribundus. Stern. Dissociated. Fibres in different stages of cavity forma­ tion. - 4 & 5: Fibres with forking branches (arrow). - 6: Two superimposed fibrt<s, suggesting the presence of a cavity (arrow). -7: The two superimposed fibres (Fig. 6) separated; one fibre has a concavity (arrow) and the other has the mold of the concavity (*). - 8: Concavity on the fibre (arrow). - 9: Fibre with different stages in the formation of the cavity; concavity present (arrow); contact of two adjacent walls (*); cavity formed (C). - 10: Detail of Fig. 9: fibre with contact of two adjacent walls (*); cavity formed (C). - 11: Two cavities in one fibre (C). Downloaded from Brill.com09/28/2021 12:59:18PM via free access.