台灣蘆竹葉部之形態及表皮組織之發育

Abstract

本篇探討台灣蘆竹(Arundo formosana Hack.)之葉部形態，葉片各細胞之構造，葉部之形態發生，並特別關注葉片表皮細胞之發育過程． 台灣蘆竹葉之表皮是由長型細胞，短型細胞（分為矽質細胞和木栓細胞），氣孔複合體，氣孔間細胞，泡狀細胞與毛茸（分為刺毛和微毛）等所組成．這些細胞在葉鞘和葉片排列有規則性，形成不同的細胞帶．葉舌膜狀，上緣佈滿毛茸． 長型細胞與泡狀細胞高度液胞化，胞器極少．矽質細胞啞鈴形，胞內幾乎為矽質體佔據．木栓細胞扁啞鈴形或長淺裂形，細胞內液胞化程度小，胞器較多．氣孔複合體包括一對保衛細胞，一對副細胞和開口．保衛細胞為長骨頭狀，內外側皆有細胞壁突板．細胞中央部分壁厚，而兩端壁較薄．內部胞器豐富，以粒線體最多．核亦如同其細胞形狀，葉綠體只分佈於細胞兩端．細胞兩端間具不完整細胞壁，細胞質可相互流通．副細胞紡綞狀，細胞內有大液胞，但胞器仍多．微毛含有頂端細胞與基部細胞，成熟時，頂端細胞萎縮或脫落．基部細胞液胞少，胞器多，尤其是粒線體，內質網和高爾基氏體．核為長條形． 葉肉組織含葉肉細胞，無色細胞與厚壁細胞．葉肉細胞長深裂形，內含大量葉綠體．無色細胞淺裂形或長方形，高度液胞化，僅有少許葉綠體．厚壁細胞形最小． 葉為平行脈，有脈間脈連接．除中央脈外，縱行脈可分為大型脈與小型脈，主要區別在前者有兩個大型的導管細胞和早成木質部空腔，而後者沒有．維管束組織外有兩層束鞘細胞包圍，外鞘細胞較大而壁薄，內鞘細胞小而壁厚．內，外鞘細胞皆高度液胞化．外鞘細胞有葉綠體，內鞘細胞則無．脈間脈由3-5列管胞構成，次生細胞壁螺旋狀加厚． 枝梢頂端分生組織具單一層表皮分裂層和單一層下皮層．葉之起源為表皮分裂層行平周分裂，接著下皮層行平周分裂．葉原之側面生長由邊緣和次邊緣始源細胞參與，而導致兩側邊緣重疊． 同一枚葉內之中央脈最先形成，然後依次由其兩鄰之葉脈向葉綠方向逐漸形成．中央脈起源於葉原突起位置一個具高度分生能力且少液胞的始原細胞，經行不同方向之分裂而形成原維管束組織（原始形成層），此組織隨著發育而向上下延伸．側脈發育亦如同中央脈，唯始源細胞有較多液胞．外鞘源位於圍繞原維管束組織之基本組織內，而內鞘則源於原維管束組織之最外層．脈間脈源於內鞘細胞，起源時內鞘細胞尚未厚壁化． 小型原始表層細胞之衍生物行一次不均等分裂後，較大的細胞分化成矽質細胞，較小的細胞分化成木栓細胞．長型細胞則源於大型原始表層細胞．氣孔源於大型原始表層細胞，經行一次不均等分裂後，大且質淡者為氣孔間細胞母細胞；小且質濃者為保衛細胞母細胞．保衛細胞母細胞形成後，其兩旁之原始表層細胞形成一扁豆狀突起，是為副細胞．保衛細胞母細胞則行縱向分裂而形成兩個保衛細胞．原始表層細胞之衍生物膨大且逐向外突出，細胞基部持續膨大但頂端變尖者，形成刺毛；而細胞伸長且行分裂者，則形成微毛．泡狀細胞之起源時期與脈之形成有關，先發育的脈，其旁先有泡狀細胞的生成．泡狀細胞的膨大方向受厚壁細胞形成之限制．泡狀細胞的膨大，間接造成葉的展開．

The morphology, cellular structure and ontogeny of leaf, with special reference to epidermis, were examined for Arundo formosana Hack.. The leaf epidermis of Arundo formosana Hack. is composed of long cell, short cell, stomatal complex, interstomatal cell, bulliform cell and trichome. The cells in epidermis are arranged regularly and form several zones in both sheath and blade. The ligule is membranous. Long cells and bulliform cells are the most vacuolated among all cell types in epidermis. The organelles are very few. Silica cells appear to be as a dumb-bell, and cell lumen is occupied by silica bodies. Cork cell exhibit as flat-dumb-bell, less vacuolated and with more organelles. The stomatal complex contains two guard cells, two subsidiary cells and aperture. Guard cell pocesses both outer and inner ledages. The cell wall in the central part of the guard cell is thickened, but that in the bulbous end is thinner. The organells are rich and mitochondria are the most abundant. The chloroplasts and the vacuoles are distributed in the bulbous ends only. The incomplete wall is found in the wall located between two guard cells in their bulbous ends. It results in the migration of organelles of two contiguous guard cells. The subsidiary cells are more vacuolated than the guard cells. The mesophyll consists of mesophyllous cell, colorless cell and the sclerenchyma. The mesophyllous cell is long-deep-lobed, containing many chloroplasts. The colorless cell shows the most vacuolated containing a few chloroplasts. Intercostal veins are formed located between two longitudial veins. In addition to medium veins, the longitudial veins can be identified as major and minor veins. The indication of the former is the presence of two large sieve tube members and one protoxylem lacuna. The vascular strand is surrounded by biseriate sheath cells. The outer sheath cells are larger and thin-walled, whereas the inner sheath cells appear to be smaller and thick-walled. Each intercostal vein consists of 3-5 files of spiral thickening tracheids. The dermatogen and hypodermis are found in the shoot apex. The leaf primordium is formed by a series of periclinal divisions in the dermatogen together with the subsequent periclinal divisions of hypodermal cells. The lateral growth of the leaf primordium causes the lateral overlapping of leaf margins. The median vein is the first vein forming in the leaf primordium, then the differentiation of lateral veins proceeds outwards the leaf margin. The median vein is initiatd in a single initial cell at the disc of inseration. It divids in various directions to form a cluster of cells, procambium. The procambial strand extends both acropetally and basipetally from the original seat, and becomes in connection with the other vascular strand of the plant. Development of the lateral veins shows similar pattern as that in median vein, but its initial is more vacuolated. It is located above the disc of inseration. The outer leaf sheath differentiates in ground meristem, but the inner sheath in the outermost layer of the procambium. The intercostal veins initiated in inner sheath cells. At the time of initiation the inner sheath cells are still in thin-walled stage. After several divisions the small protodermal cells divids unequally. Its larger derivative gives rise to silica cell and the smaller one to cork cell. Some large protodermal cells become large cells, and some divide unequally. Its large derivative differentiates into interstomatal cell initial and small one into guard cell mother cell. The subsidiary cells occur perigenously. Still some other protodermal cells become protruded outwards as trichomes. The direction of bulliform cell enlargement is limited by the presence of sclerenchyma beneath it. The enlargement of bulliform cell would play a role in expansion of blade.