楓樹幼枝形成層之季節性活動情形

Abstract

本文主要研究生長在自然環境下之楓樹(Liquidambar formosana Hance)其形或層之季節性活動情形及其內部構造之形態與發生。 楓樹之形成層活動受氣溫之影響頗大，二月時氣溫最低，僅14.8℃，三月開始逐漸上昇至加16.9℃,形成層也開始活動，到了四月昇至21.4℃，形成層帶之細胞可多達六層，五、六、七月氣溫繼續上昇，形成層之活動一直很旺盛，八月開始活動力逐漸減低，至十月下旬停止活動。降雨量及相對濕度對形成層之活動似乎並無影響。從楓樹外型之變化上看來，頂芽之發生與形成層之活動有密切之關連。 在春天形成層活動開始時，?皮部紙胞之分化比木質部為早，但比木質部先停止分化糸，於每年三月初即開始分化，木質部則於三月底或四月初才開始分化。?皮部在產生之當年冬季即失去功用。它具有篩管細胞、伴細胞及薄壁細胞，薄壁細胞中 有許多多面體結晶。 木栓形成層之股生很早，在小枝產生之第一年即可見到。木栓形成層源於表皮下皮層之第一層細胞，它的活動力可持續很久，向內產生之栓皮比向外產生之木栓層為少。皮孔之形成約在四月至七月。 皮層所含之細胞種類極為複雜，除薄壁細胞外尚有石細胞及纖維，纖維恰位於皮層與?皮部之間，形成二者之界限，薄壁細中具有三種形狀不同之晶體，即晶簇狀結晶、多面體結晶及結晶砂，其中以晶簇狀結品最為常見。 後生木貿部屬於散孔材，薄壁細胞很少，屬於離管薄壁細胞中之散狀薄壁細胞，具單層射線及多層射線。導管長約77Oμ-85Oμ，具有梯狀穿孔板。在七年老之莖中可見導管細胞內有填充細胞之形成。 髓部為不規則之多角形，細胞初為薄壁細胞後變為厚壁細胞，細胞內有許多澱粉粒及少數結晶。此外髓部還具有許多樹膠管，樹膠管之發生很早，在距頂端0.2mm處即已開始分化，初形成時非常靠近初生木質部，管內上皮細胞之功用可維持六、七年之久。

This investigation deals primarily with the seasonal activity of the cambium of the stem of Liquidambar formosana Hance. The morphological changes of the stem associated with cambial activity were observed. Cambial activity is affected mainly by temperature. In February, the average monthly temperature was only 14.8°C, and the cambium is dormant, while in March, the temperature rises to 16.9°C, and cambium activity is initiated in late March, as temperature increases, cambial activity inereases till July, and then slowly declines and ends in October. Rainfall and relative humidity possibly have no effects on cambial activity. In view of its relation with phenclogy, it seems possible that there is a correlation between, actively growing buds and the initiation of cambial activity. The phellogen originates in the early developmental stage of the stem. It arises in the suhepidermal layer of one-year-old stems and produces less phelloderm cells inwardly than phellem cells outwardly. From April to July, developing lenticels are seen on the stem. The first periderm may be retained for many years. The cortex is made up of parenchyma, brachysciereids and. fibers, which delimit the certex and the paloem. Three kinds of crystals are found in the cortical parenchyma: druses, prismatics and crystal sands. Among them the most common are druses. Phloem elements differentiate in early March, and cease their function in the same season. The elements in the axial system cunsist of sieve-tube members usually with companin cells and axial parenchyma cells with many prismatic. The wood is diffuse porous with both uniseriate and muitiseriate rays. Axial parenchyma s distributed very sparsely. It beloogs to the diffuse arrangement of the apctracheal type. The vessels have scalariform perferation plates and tylosess can be found in vessels of six-or seven-year-old stems. Pith is polygonal in shape, with parerchyma in the early stages which become scierified later. The pith cells contain numerous starch grains and a few crystals. Gum ducts begin to differentiate near the protoxylem group at aboct 0.2mm from the apex. The epithelial cells function for six or seven years.