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標題: | 雀榕離層區的形成和形成層的活動 Formation of Abscission Zone and Cambial Activity in Ficus wightiana Wall. ex Benth. |
作者: | Shau-ting Chiu 邱少婷 |
出版年 : | 1986 |
學位: | 碩士 |
摘要: | 本報告?述雀榕(Ficus wightiana Wall. ex Benth.)之落葉過程中,葉柄離層區組織之變化,以及同時期內管束形成層之活動與落葉之相關性。 雀榕莖解剖由外向內包括表皮、周皮、皮層、維管束組織及髓等組織,其維管束乃並生型,屬於?正中軸。形成層很早就發育並連成圈,以七、八月(月均溫最高時)分裂活動最旺盛,十二、一月(月均溫最低時)最不活躍;其所形成之次生木質部的細胞層數比次生?皮部者多。因其全年均有分裂活動,故衍生之木質部生長輪不明顯,木材?散孔材,含大量離管帶狀和順管群流的縱行薄壁細胞,心材具?充細胞。 落葉時期在早春三、四月之間,抽芽第一次在四、五月,第二次則在七月;冒芽前頂芽鱗片先落,新芽抽長後白色托葉立刻脫離;隱頭花序十一月形成,落果期在三至五月。 當五至六月新葉形成時,離層區乃由小而質濃的細胞所組成,但離層與初生保護層尚不能辨認;七月到十一月離層組織發生不規則細胞分裂由外圍向中心逐漸形成,離層區草酸鈣結晶增加,管細胞的?充細胞出現,且十月後開始木質一木栓化,初生保護層於是形成;十二月到次年四月離層細胞分裂伴隨細胞間隙擴大、中膠層解體使細胞間鬆離而由葉腋處先產生裂痕,漸趨擴延至表皮及維管束附近;離層發育成熟後,葉片藉風力、觸碰等機械力脫落,於是初生保護層裸露,斷面細胞排列不規則,其後在內側有一整帶的細胞經平周分裂形成次生保護層,與莖周皮連成一片。 在七月離層區開始有細胞分裂時,形成層也正?細胞分裂最旺盛的時期,頂芽剛好第二次抽長;十二月離層裂痕出現,而形成層活動卻趨於平緩,直到三、四月離層發育成熟促成葉落,形成層則重新開始活躍。 其植物體內常見的特殊構造有乳汁管、含酚類化合物的細胞、單寧細胞、草酸鈣結晶的細胞以及木質—木栓化的現象;在早期離層區內細胞的酚類化合物含量高,且存在一些單寧細胞,但未見乳汁管之通過及草酸鈣結晶的出現,隨著離層細胞的發育,酚類化合物含量降低,單寧細胞減少,草酸鈣結晶出現漸多,且晚期離層區內之初生保護層細胞之木質一木栓化現象,漸趨顯明。 The present investigation deals with the histological changes within the abscission zone of Ficus wightiana Wall. ex Benth. during the process of leaf abscission. The cambial activity correlated with the leaf abscission was also examined. The stem anatomy of Ficus wightiana consists of epidermis, periderm, cortex, vascular tissue and pith centripetally. The vascular bundles are collateral and arranged in eustelic pattern. The vascular cambium develops early and becomes a complete cylinder. The cambium is very active in July and August, as the high average monthly temperature. On the other hand, it becomes inactive when the average monthly temperature is low in December and January. The number of cell divisions in cambium resulting in the formation of secondary xylem exceeds those that give rise to secondary phloem cells. The growth rings of wood are not obvious. The wood shows diffuse-porus type, and axial parenchyma appear in both banded apotracheal and confluent paratracheal patterns. Vessels in the heart wood filled with tyloses. Leaf abscission occurs in early spring in March to April. The first bud sprouting occurs in April to May. The second sprouting appears in July. Scales of the bud shed before bud sprouting. New twig elongates as soon as white stipules fall. The formation of hypanthodia commences in November and the abscission occurs from March to May. When juvenile leaves appear in May and June, small and densely stained cells occupy the abscission zone, but the separation layer and protective layer cannot be identified from each other. Irregular cell divisions appears within abscission zone centripetally in July to November. Of the same period, calcium oxalate crystals increase and tyloses become protruded in the lumens of tracheary elements. In October, ligno-suberization initiates in abscission zone, consequently forms the primary protective layer. From December to April in next year, the cell divisions in separation layer are accompanied with the enlargement of intercellular space as well as the lysis of middle lamella. This process results in formation of the crack near the leaf axil. The separation extends towards both epidermis and vascular strands. When separation layer becomes well organized, leaf abscission is facilitated merely by wind or force of touch. Eventually the primary protective layer would be exposed to the air. The cells on the separate surface are arranged irregularly. Finally layer of cells beneath the leaf scar begin periclinal divisions and give rise to secondary protective layer which becomes continuous with the periderm of the stem in later stage. When cell divisions begin in the abscission zone in July, it is just the time the cambium characterized by a highly active stage and the second time for the bud sprouting. The crack in the separation layer apears in December. Nevertheless cambium reveals inactive. Till March and April, separation layer is accomplished and brings about the leaf shedding. It is found that the cambial activity is initiated at the time of leaf falling. Several obvious structures usually existing in the plant tissues are laticifers, phenolic compounds containing cells, tannin containing cells, the cells with calcium oxalate crystals, and ligno-suberized cells. In the early stage of the formation of abscission zone, there is a high frequency of phenolic compounds containing cells, as well as the tannin containing cells in the abscission zone. But no laticifers and calcium oxalate crystals were observed. Following the development of abscission zone, the contents of phenolic compounds in cells decrease, tannin containing cells diminish, and calcium oxalate drystals increase. The lingo-suberized cells in the primary protective layer within the abscission zone become obvious in a later stage. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/75572 |
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顯示於系所單位: | 植物科學研究所 |
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