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Comparative Anatomy of Resin Ducts of the Pinaceae

Comparative Anatomy of Resin Ducts of the Pinaceae

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Trees (1997) 11: 135–143  Springer-Verlag 1997

ORIGINAL ARTICLE

Hong Wu c Zheng-hai Hu gomp—r—tive —n—tomy of resin du™ts of the €in—™e—e

Received: 12 September 1995 / Accepted: 14 March 1996

AbstractmResin ducts are common in the . The these studies are limited to a specific or organ. A comparative anatomy of stems and of 50 and systematic investigation on the comparative anatomy of two varieties from ten genera has been investigated. The resin ducts of Pinaceae has not been undertaken. Previous structure and distribution of resin ducts differ among studies have shown that the structure and distribution of genera. Resin ducts occur in foliage leaves of ten genera resin ducts are different between different genera; therefore, of Pinaceae. Cortical resin ducts are absent in the stems of comparative studies on resin ducts of the Pinaceae have Pseudolarix and Larix. Resin ducts only occur in the great significance in theory. The present paper systemati- secondary xylem of stems of Pinus, Picea, Cathaya, cally compares the structure and distribution of resin ducts Larix, and some species. All of in the stems and leaves of ten genera of Pinaceae and the epithelial and sheath cells are alive and thin-walled in discusses generic relationships. the resin ducts of stem cortex and mesophyll. Except for Pinus the epithelial cells of resin ducts in the secondary xylem of stems have thick, lignified walls. Comparative

study shows there are obvious differences in the resin ducts of different genera; apparent differences do not exist, w—teri—ls —nd methods however, in the resin ducts of different species of the Experimental materials included 50 species and two varieties of ten same genus. According to the structure and distribution of genera of Pinaceae. Species and locations are as follows: the resin ducts in ten genera of Pinaceae, a synoptical arrangement of the genera is given and generic relation- Genus Species Locations ships of the Pinaceae are discussed. 1. Keteleeria Carr. K. cyclolepis Flous Guangxia K. davidiana (Franch.) Beiss. Zhejianga

K. evelyniana Mast Yunnana c Key wordsmComparative anatomy c Pinaceae Resin duct K. fortunei (Murr.) Carr. 2. Abies Mill. A. chensiensis v. Tiegh Shaanxi

A. ernesti Rehd. Sichuana sntrodu™tion A. fabri (Mast.) Craib Jiangxi A. fargesii Franch Shaanxi A. faxoniana Rehd. et Wils. Sichuana The Pinaceae is the largest of with A. firma Sieb. et Zucc. Jiangxi ten genera and 230 species distributed all over the world; A. georgei Orr Yunnana there are ten genera and approximately 90 species in A. holophylla Maxim. Jilina (Cheng et al. 1978). Some information has been reported on A. nephrolepis (Trautv.) Maxim. Shaanxi the structure, distribution and development of resin ducts in A. sutchuenensis (Franch.) Shaanxi Rehd. et Wils. the Pinaceae (Hanes 1927; Mergen and Echols 1955; Werker and Fahn 1969; Fahn 1979; Wu et al. 1987; Wu 3. Pseudotsuga Carr. P. gaussenii Flous Jiangxi 1990). A few references are also available on the compara- P. sinensis Dode Jiangxi tive anatomy of the resin ducts (Bannan 1936; Greguss 4. Tsuga Carr. Sect. Heopeuca Kang et Keng f. Guang- 1955; Gui and Lee 1963; Lee and Mu 1966; Jain 1976), but T. longibracteata Cheng donga Sect. Tsuga T. chinensis (Franch.) Pritz Shaanxi

T. chinensis var. tchekiangensis Jiangxi Hong Wu ( ) c Zheng-hai Hu (Flous) Cheng et L. K. Fu Institute of , Northwest University, Xi’an 710069, People’s T. dumosa (D. Don) Eichler Yunnana Republic of China T. forrestii Downie Yunnana ______中国科技论文在线 www.paper.edu.cn

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Genus Species Locations distribution of the resin ducts of different genera of Pina- ceae are different. 5. Cathaya Chun et C. argyrophylla Chun et Kuang Kuang 6. Picea Dietr. Sect. Picea Structure and distribution of the resin ducts of each P. abies (Linn.) Karst Jiangxi Pinaceae genus P. asperata Mast Shaanxi P. crassifolia Kom. Ninxiaa P. koraiensis Nakai Jilina Keteleeria Carr. P. wilsonii Mast Jiangxi Sect. Casicta Mayr The resin ducts are distributed in stem cortex and meso- P. likiangensis (Franch.) Pritz. Yunnana P. purpurea Mast. Qinhara phyll. Cortical ducts occur in the central portion of the Sect. Omerica Willk cortex (Fig. 1). In the needles, two lateral, abaxial ducts P. brachytyla (Franch.) Pritz Shaanxi appear in the mesophyll, one each on both sides of the 7. Larix Mill. L. chinensis Beissn Shaanxi paralleling the long axis of the (Fig. 3). L. gmelini (Rupr.) Rupr. Heilong- Both epithelial and sheath cells are alive and thin-walled. In jianga addition, vertical resin ducts occur in the secondary xylem L. griffithii Hook. f. Yunnana of stems in K. davidiana (Fig. 2) and K. evelyniana. Their L. kaempferi (Lamb.) Carr. Jiangxi 2 L. mastersiana Rehd. Sichuana distribution density is 0.37 –2.5 ducts/mm . Almost all L. olgensis Henry var. koreana epithelial and sheath cells have thickened, lignified walls. Nakai Jilina L. potaninii Batal. Sichuana L. principis-rupprechtii Mayr Jiangxi L. sibirica Ledeb. Xinjianga Abies Mill. 8. Pseudolarix P. amabilis (Nelson) Rehd. Jiangxi The resin ducts are distributed in stem cortex and meso- Gord. phyll. Cortical ducts occur in the central portion of the 9. Cedrus Trew C. deodara (Roxb.) Loud. Shaanxi cortex (Fig. 4). In the needles, there are either two resin 10. Pinus Linn. Subgen. Strobus (Sweet) Rehd. ducts (A. chensiensis, A. ernestii, A. fargesii, A. faxoniana, P. armandi Franch. Shaanxi A. georgei, A. holophylla, A. nephrolepis, A. sutchuenensis) P. bungeana Zucc. ex Endl. Shaanxi or four resin ducts (A. fabri, A. firma; Fig. 5). In the former, P. koraiensis Sieb. et Zucc. Liaonina Subgen. Pinus two lateral, abaxial or middle ducts appear in mesophyll; in P. densiflora Sieb. et Zucc. Liaonina the latter, four ducts, divided into groups of two, are P. elliottii Engelmann Hainan distributed on both sides of vascular bundle. Both epithelial P. finlaysoniana Wall. Hainan and sheath cells are alive and thin-walled. P. massoniana Lamb. Sichuana P. tabulaeformis Carr. Shaanxi P. taiwanensis Hayata Anhuia P. thunbergii Parl Zhejianga Pseudotsuga Carr. P. yunnanensis Franch. Yunnana a Collected from herbarium of WNU and WUG The resin ducts are distributed in the cortex, primary xylem, and secondary xylem of stems and in the mesophyll. Cortical ducts occur in the outer portion of cortex (Fig. 6). Fresh material of 26 species was directly fixed in FAA (formalin-

acetic acid-alcohol). Herbarium material of 26 other species was steeped in distilled water for several days, then fixed in FAA. Leaves, R including parts from tip, median, and base, and juvenile stems were Figs. 1–12m1 Cross-section of juvenile stem of dehydrated through an alcohol series and embedded in paraffin wax. showing distribution of cortical ducts. 2 A cross-section of of K. The samples were sectioned at 8–12 µm thickness. Wood from davidiana showing distribution of vertical ducts of the secondary trunks was boiled in water for 2 h, then softened in glycerine and 95% xylem. 3 A cross-section of leaf of K. fortunei showing distribution alcohol (1:1) for several weeks. Cross, radial and tangential sections of of ducts in mesophyll (arrow). 4 A cross-section of juvenile stem of the wood were obtained with a sliding microtome at 20–40 µm Abies fabri showing distribution of cortical ducts. 5 A cross-section of thickness. Sections were stained with safranin and fast green, sealed leaf of A. fabri showing distribution of ducts in mesophyll (arrows). in Canada balsam, and observed under an Olympus microscope. 6 A cross-section of juvenile stem of , showing distribution of cortical ducts. 7 Cross-section of wood of P. sinensis showing distribution of vertical ducts of the secondary xylem. 8 A longitunal (tangential) section of wood of P. sinensis showing distri-

bution of horizontal ducts of the secondary xylem. 9 A cross-section of ‚esults leaf of P. sinensis showing distribution of ducts in mesophyll (arrow). 10 A cross-section of juvenile stem of Tsuga chinensis showing The resin ducts are schizogenously formed in the stems and distribution of cortical ducts. 11 A cross-section of leaf of T. chinensis leaves of the Pinaceae. Mature ducts are elongated struc- showing distribution of duct in mesophyll (arrow). 12 A cross-section of juvenile stem of Cathaya argyrophylla showing distribution of tures consisting throughout their length of epithelial cells cortical ducts. Bars indicate 500 µm. D, Dead sheath cell; E, Epithelial surrounding an intercellular space and on their outer side of cell; HR, Horizontal duct; L, Epithelium with lignified wall; Rd, Resin one to three layers of sheath cells. The structure and duct; T, Epithelium with thin wall; VR, Vertical duct ______中国科技论文在线 www.paper.edu.cn

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Figs. 13–23m13 A cross-section of wood of C. argyrophylla showing section of leaf of P. wilsonii showing distribution of ducts in mesophyll distribution of vertical ducts of the secondary xylem. 14 A longitudinal (arrows). 20 A cross-section of juvenile stem of Larix kaempferi (tangential) section of wood of C. argyrophylla showing distribution of showing cyst-like vesicle (arrow) in cortex near phloem. 21 A cross- horizontal ducts of the secondary xylem. 15 A cross-section of leaf of section of wood of L. kaempferi showing distribution of vertical ducts C. argyrophylla showing distribution of ducts in mesophyll (arrows). of the secondary xylem. 22 A longitudinal (tangential) section of wood 16 A cross-section of juvenile stem of Picea wilsonii showing of L. kaempferi showing distribution of horizontal ducts of the distribution of cortical ducts. 17 A cross-section of wood of P. wilsonii secondary xylem. 23 A cross-section of leaf of L. kaempferi showing showing distribution of vertical ducts of the secondary xylem. 18 A distribution of ducts in mesophyll (arrows). (Fig. 22, bars indicate longitudinal (tangential) section of wood of P. wilsonii showing 200 µm; other figures, bars indicate 500 µm. Other symbols as distribution of horizontal ducts of the secondary xylem. 19 A cross- Figs. 1–12) ______中国科技论文在线 www.paper.edu.cn

139 The epithelial and sheath cells are alive and thin-walled. In Picea Dietr. P. gaussenii Flous, the resin ducts occur in primary xylem, each vascular bundle has one or two ducts, and a large The resin ducts are distributed in cortex and secondary proportion of the duct cells have thickened, lignified walls. xylem of stems and in the mesophyll. Cortical ducts occur Vertical and radial resin ducts appear in the secondary in the central portion of stem cortex (Fig. 16). Both xylem of stems (Figs. 7, 8). The vertical ducts are concen- epithelial and sheath cells remain alive and thin-walled. trated in the outer region of the early wood and in the first- Vertical and radial ducts occur in the secondary xylem of formed late wood. The average number of resin ducts per stems (Figs. 17, 18). Vertical ducts are in the outer region of square millimeter is 0.6 in P. gaussenii and 4.1 in P. early wood and first-formed late wood, the number of ducts sinensis. More than 80% of the epithelial cells have per square millimeter being 2.4–3.5. More than 80% of the thickened, lignified walls; some become dead cells. All epithelial cells have thick, lignified walls (Fig. 34), and sheath cells form thickened, lignified walls. Some sheath some lack protoplasts at maturity. Sheath cells have thick, cells remain alive for several years. A small number of lignified walls; some cells remain active for several years. radial ducts appear in xylem rays, the average number of Radial resin ducts occur in xylem rays; there are 0.3–0.4 radial ducts per square millimeter varying from 0.15 to ducts/mm2. The epithelial cells are thin- or thick-walled and 0.20. The epithelial cells are either thin-walled or with lignified; sheath cells have thick, lignified walls. In the thickened, lignified walls. In the needles, two lateral, needles, one or two resin ducts occur in the outer portion of abaxial ducts occur in mesophyll (Fig. 9). Both epithelial leaves (Fig. 19). Both epithelial and sheath cells are alive and sheath cells remain alive and thin-walled. and thin-walled.

Larix Mill. Tsuga Carr. The resin ducts are distributed in the secondary xylem of The resin ducts are distributed in stem cortex and meso- stems and in the mesophyll. Resin ducts are absent in stem phyll. Cortical resin ducts occur in either the outer or cortex. Sometimes a few cyst-like vesicles are formed in central portion of cortex (Fig. 10). In the needles, one the cortex from enlarged ends of radial ducts (Fig. 20). abaxial duct occurs under the vascular bundle (Sect. Heo- Vertical and radial resin ducts occur in the secondary xylem peuea) or within the vascular bundle between bundle sheath (Figs. 21, 22). Vertical ducts are primarily concentrated in cells (Sect. Tsuga; Fig. 11). Large parenchyma cells border late wood, the number of ducts per square millimeter the epithelial cells externally; sheath cells are not obvious. ranging from 2.5 to 2.8. More than 90% of the epithelial In addition, normal scattered ducts are absent in the cells have thickened, lignified walls, and most of them lack secondary xylem of the stem. Traumatic ducts occur in protoplasts at maturity. Sheath cells form thick, lignified the secondary xylem of stems of T. longibracteata. They are walls; some of these cells are dead. Radial resin ducts distributed in the early wood, arranged in a circle forming appear in xylem rays; their distribution density is 0.15–0.7 tangential anastomosis of ducts. Their epithelial and sheath ducts/mm2. About 70% of the epithelial cells have thick- cells all have thickened, lignified walls. ened, lignified walls and some cells are dead. In the needles, two resin ducts occur in the mesophyll, but there is only one duct along each leaf margin (Fig. 23). Both Cathaya Chun et Kuang epithelial and sheath cells are alive and thin-walled. The resin ducts are distributed in the cortex and secondary xylem of stems and in the mesophyll. Cortical ducts occur Pseudolarix Gord. in the inner portion of the cortex near the vascular cylinder (Fig. 12). Both epithelial and sheath cells remain alive and Resin ducts occur only in mesophyll (Fig. 25), with a thin-walled. Vertical and radial ducts occur in the secondary lateral, abaxial resin duct near each margin and one abaxial xylem of the stems (Figs. 13, 14). The former appear in the resin duct under the vascular bundle. Both epithelial and outer region of early wood and in the first-formed late sheath cells remain alive and thin-walled. Resin ducts are wood, their distribution density being 0.32 ducts/mm2. absent in the stem cortex (Fig. 24). Approximately 80% of epithelial cells have thickened, lignified walls; some become dead cells. All of the sheath Cedrus Trew cells have thickened, lignified walls and almost all become dead cells. Radial ducts occur in xylem rays, the number of The resin ducts are distributed in stem cortex and meso- radial ducts per square millimeter being 0.7. Seventy per phyll. Cortical ducts are in the inner portion of cortex and cent of the epithelial cells form thickened, lignified walls; near to the vascular cylinder (Fig. 26). In the needles, two all sheath cells have thickened, lignified walls. In the lateral, abaxial resin ducts appear in mesophyll (Fig. 28). needles, two lateral, abaxial ducts are distributed one Both epithelial and sheath cells are alive and thin-walled. each on both sides of the vascular bundle and near to the Normal ducts are absent in the wood, but traumatic ducts margins (Fig. 15). Both epithelial and sheath cells are alive are present in the early wood arranged in a circle forming and thin-walled. tangential anastomosis of ducts (Fig. 27). Among them, a ______中国科技论文在线 www.paper.edu.cn

140 few epithelial and sheath cells have thickened, lignified 2. Vertical resin ducts are present in cortex of stems walls. 3. In resin ducts of wood of stems, epithelial cells are alive and thin-walled ...... Pinus Pinus Linn. 3. In resin ducts of wood of stems, epithelial cells have thickened, lignified walls The resin ducts are distributed in the cortex, primary xylem, 4. Cortical resin ducts occur near to vascular and secondary xylem of stems and the mesophyll. Cortical bundles ...... Cathaya ducts occur in various portions (inner, central and outer; 4. Cortical resin ducts occur in the outer portion or the Fig. 29); both epithelial and sheath cells are alive and thin- central portion of cortex walled. Some species have resin ducts in the primary 5. Cortical resin ducts occur in the outer portion of xylem, with one or two resin ducts per vascular bundle. cortex ...... Pseudotsuga Whereas the epithelial cells are alive and thin-walled, the 5. Cortical resin ducts occur in central portion of sheath cells have relatively thick walls and some sheath cortex cells are dead. Vertical and radial ducts occur in the 6. Radial resin ducts are present in the secondary secondary xylem (Figs. 30, 31); there are vertical ducts in xylem of stems ...... Picea the outer region of early wood and first-formed late wood. 6. Radial resin ducts are absent in the secondary The number of ducts per square millimeter is 4–5. Their xylem of stems ...... Keteleeria epithelial cells also remain alive and thin-walled; the sheath (K. davidiana, K. evelyaniana) cells have thicker walls than epithelial cells (Fig. 33). Some 1. Normal, scattered resin ducts are absent in the secondary sheath cells lack protoplasts at maturity. Radial ducts occur xylem of stems in xylem rays, with a distribution density of 0.5–2 ducts/ 7. One resin duct occurs in mesophyll ...... Tsuga mm2. Some of their sheath cells are also dead. In the 7. More than one resin duct occurs in mesophyll needles, the resin ducts of mesophyll occur along the 8. Three resin ducts occur in mesophyll . Pseudolarix margin (P. bungeana, P. densiflora, P. massoniana, P. 8. Two or four resin ducts occur in mesophyll tabulaeformis) or central portion of the leaves (P. koraien- 9. Cortical resin ducts occur in the inner portion of sis, P. taiwanensis, P. thunbergii, P. finlaysoniana), or near stem cortex and near to vascular bundles . Cedrus to bundle sheaths (P. elliottii). In addition, resin ducts occur 9. Cortical resin ducts occur in the central portion of on the margin and central portion of leaves at the same time stem cortex in P. armandi (Fig. 32) and P. yunnanensis. There are 2–3 10. Diameter of cortical resin ducts is large; a few ducts in the mesophyll of subgen. Strobus, and 2–12 ducts sheath cells contain tannin substance; two or four in the mesophyll of subgen. Pinus. Both epithelial and resin ducts occur in the mesophyll, one each on sheath cells are alive and thin-walled. either side of the vascular bundle or one both along the margins and on either side of the bundle in the central portion of the leaf ...... Abies Differences of resin ducts among different genera of 10. Diameter of cortical resin ducts is small; a large Pinaceae and synoptical arrangement of the ten genera number of sheath cells contain tannin substance; two resin ducts occur in mesophyll, one each According to comparative anatomical study of stems and along the margins of the leaves . . . . Keteleeria leaves of 50 species and two varieties of the ten genera, (K. fortunei, K. cyclolepis) resin ducts are found in the mesophyll of all foliage leaves, but the number and distribution of ducts differ among the

various genera. In stems, cortical ducts occur in eight genera, but are absent in Larix and Pseudolarix; the number R and distribution of ducts also differ among the eight genera. Figs. 24 –34m24 A cross-section of juvenile stem of Pseudolarix Resin ducts are present in the secondary xylem of Pinus, amabilis showing that cortical ducts are absent. 25 A cross-section of leaf of P. amabilis showing distribution of ducts in mesophyll Cathaya, Picea, Larix, Pseudotsuga, and some Keteleeria (arrows). 26 A cross-section of juvenile stem of Cedrus deodata species but are absent in four other genera. With respect to showing distribution of cortical ducts. 27 A cross-section of wood of the structure of resin ducts, the epithelial and sheath cells of C. deodata showing distribution of traumatic ducts (arrow) in the ducts of mesophyll and cortex are alive and thin-walled at secondary xylem. 28 A cross-section of leaf of C. deodata showing maturity. In the resin ducts of secondary xylem, only distribution of ducts in mesophyll (arrows). 29 A cross-section of juvenile stem of Pinus armandi showing distribution of cortical ducts. epithelial cells of Pinus remain alive and thin-walled; 30 A cross-section of wood of P. armandi showing distribution of epithelial cells in the resin ducts of five other genera have vertical ducts of the secondary xylem. 31 A longitudinal (tangential) thickened, lignified walls. According to the differences in section of wood of P. armandi showing distribution of horizontal ducts structure and distribution of the resin ducts, a synoptical of the secondary xylem. 32 A cross-section of leaf of P. armandi showing distribution of ducts in mesophyll. 33 A cross-section of wood arrangement of the ten genera of Pinaceae is given. of P. armandi showing structure of vertical duct of the secondary 1. Normal, scattered resin ducts are present in wood of xylem; epithelial cells remain alive and thin-walled. 34 A cross-section stems of wood of Picea wilsonii showing structure of vertical duct of the secondary xylem; epithelial cells have thickened, lignified walls. 2. Vertical resin ducts are absent in cortex of (Figs. 24 –32, bars indicate 500 µm; Figs. 33, 34, bars indicate stems ...... Larix 200 µm. Other symbols as Figs. 1–12) ______中国科技论文在线 www.paper.edu.cn

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dolarix, Keteleeria, Cedrus, and Tsuga; resin ducts in the his™ussion secondary xylem and leaves with endodermis having thick- ened Casparian strips support monophyly of Cathaya, Distribution of the resin ducts of stems and leaves Pinus, Larix, Pseudotsuga, and Picea. By comparing mor- of Pinaceae phologic structure of vegetative and reproductive organs in the Pinaceae, Frankis (1989) divided Pinaceae into four Hanes (1927) reported that resin ducts appearing in the subfamilies: subfamily Pinoideae (Pinus), subfamily Pi- primary body are a normal feature. Fahn (1979) ceoideae (Picea), subfamily Laricoideae (Larix, Cathaya, indicated that in the Pinaceae resin ducts appear as a normal Pseudotsuga), subfamily Abietoideae (Abies, Cedrus, Pseu- feature in the secondary body of Pinus, Picea, Larix, and dolarix, Keteleeria, Nothotsuga, Tsuga). Pseudotsuga. These ducts are the scattered and dispersed By comparing stems and leaves of 50 species and two . In Abies, Cedrus, Tsuga and Pseudolarix, the resin varieties of the Pinaceae we divided the Pinaceae into three ducts are produced only as a result of injury (traumatic groups, according to the presence or absence of resin ducts ducts). According to comparative anatomy of stems and in the secondary xyelm: normal resin ducts are present in leaves of 50 species and two varieties of ten genera of the secondary xylem of Cathaya, Pinus, Larix, Pseudo- Pinaceae, the resin ducts occur in foliage leaves; in the tsuga, and Picea; normal resin ducts are absent in the primary structure of stems, cortical resin ducts are present secondary xylem of Abies, Pseudolarix, Cedrus, and in eight genera and absent in Larix and Pseudolarix; the Tsuga; normal resin ducts are present or absent in the resin ducts of primary xylem occur only in Pseudotsuga secondary xylem of Keteleeria. We arranged Keteleeria and Pinus; vertical resin ducts are absent in phloem. In the into a single group, which belongs to neither the group with secondary xylem of stems, normal, scattered resin ducts are resin ducts in the secondary xylem nor the group without found in Pinus, Cathaya, Picea, Larix, Pseudotsuga and resin ducts in the secondary xylem. This is different from some Keteleeria species, but are absent in four other the result reported by Jeffrey (1987). With respect to genera. These findings support the viewpoint given by presence or absence of resin ducts in the secondary xylem Fahn (1979). In four other genera, normal resin ducts are of Keteleeria, Chen (1958) came to the conclusion that absent in the secondary xylem. In only Cedrus and Tsuga resin ducts are present in the secondary xylem of Kete- are traumatic ducts arranged in tangential series. So we leeria, but Jain (1976) and Jeffrey (1987) reported that resin conclude that the frequency of appearence of traumatic ducts are absent in the secondary xylem of Keteleeria. ducts is very low. According to our observations, normal vertical resin ducts With respect to the number of resin duct in leaves, are present in the secondary xylem of K. davidiana and K. Kausik and Bhattacharya (1977) and Yao and Hu (1982) evelyaniana, but are absent in that of K. fortuneii and K. separately reported that Abies leaves have two resin ducts. cyclolepis. On the basis of distribution of resin ducts – a According to our observations, in addition to this leaf type strikingly morphologic feature, Keteleeria should be locat- there are four resin ducts in the leaves of A. firma and A. ed somewhere between the group with and that without fabri, with two longer ducts along the margins and two resin ducts in the secondary xylem, but further studies of shorter ones in the central portion of leaf. Because the the systematic position of Keteleeria should be made. With distribution and number of resin ducts in leaves of Abies is respect to the systematic position of Cathaya in the Pina- very significant in , we suggest that the distribu- ceae, Xie (1957) pointed out that the genus should fit tion and number of resin ducts should be determined by between Pseudotsuga and Larix, and closer to the former comparing three (tip, median and base) portions of leaves. phylogenetically. Greguss (1970, 1972), on the other hand, indicated that, on the basis of epidermal structure of leaves and wood anatomy, Cathaya should be treated as a new Approaching generic relationships from differences species under Pseudotsuga. Hu et al. (1976) and He et al. of resin ducts in Pinaceae (1981) suggested that the systematic position of Cathaya may be located somewhere between Pinus and Picea or The family Pinaceae contains a total of ten commonly Pseudotsuga, and that Cathaya is related to genera Pinus accepted genera (Rushforth 1987; Kru¨ssmann 1985; Dalli- and Picea of the Pinaceae. Hu and Wang (1984), after more and Jackson 1966): Abies, Cathaya, Cedrus, Kete- studying the structure of various vegetative organs with the leeria, Larix, Picea, Pinus, Pseudolarix, Pseudotsuga and help of light and electron microscope, suggested that Tsuga. On the basis of leaf arrangement, the presence or Cathaya is similar in many aspects to Pseudotsuga and absence of short , and the form of and Larix. This conclusion is similar to the viewpoint of Xie pulvinus, Pilger (1926), Melchior and Werdermaan (1954) (1957) and to the classification given by Frankis (1989). divided the Pinaceae into three subfamilies: subfamily According to our results, Cathaya should be arranged in the Pinoideae (Pinus), subfamily Laricoideae (Larix, Pseudo- group with resin ducts in the secondary xylem, and the larix, Cedrus), and subfamily Abietoideae (Abies, Cathaya, systematic position of Cathaya should be between Pinus Keteleeria, Picea, Pseudotsuga, Tsuga). Jeffrey (1987) and Pseudotsuga, and closer to the latter. divided the Pinaceae into two lineages based on a few characters. The presence of resin ducts in the and of AcknowledgementsmThis work was supported by the National Nat- cleavage polyembryony support monophyly of Abies, Pseu- ural Science Foundation of China. ______中国科技论文在线 www.paper.edu.cn

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