臺灣島槐之胚胎學

Abstract

臺灣島槐(Maackia taiwanensis Hoshei et Ohashi) 屬豆科、蝶形花亞科，為台灣之特有種，落葉性喬木，花兩性，花期於八月上旬至下旬，莢果於十二月成熟。

花序原體於四月中旬在枝頂出現。花萼原體於四月下旬出現；花瓣、雄蕊、雌蕊原體於六月上旬至下旬相繼出現；花萼合生，五裂；花瓣五枚，由一枚旗瓣及各兩枚的翼瓣和龍骨瓣組成；雄蕊10支，兩輪，每一個花藥有四個花粉囊。雌蕊具單一心皮，有子房柄。 七月上旬，幼花藥，由原始表層和中央細胞團組成。花藥壁層之構成，含表皮層、一層內壁層、兩層中間層、一層營養層，藥壁層發育歸屬於基本型。營養層細胞為泌腺性型。花粉母細胞行減數分裂，細胞質分裂屬同時型，產生小孢子四分體，為四面體形。成熟花粉具二細胞，球形，三溝孔，直徑約15~20μm。花藥縱裂。 雌蕊內具2~5枚胚珠，邊緣胎座。胚珠彎生，珠被兩層，外珠被3到6層細胞厚，內珠被兩層細胞厚，於種子發育時內珠被退化。大孢子母細胞位在珠心頂端表皮細胞下四到六層細胞處，是為厚珠心。大孢子母細胞經橫向分裂後產生一直線形的大孢子四分體，之後位居合點端之大孢子發育成胚囊母細胞。胚囊發育為蓼型，兩只極核於授精前融合，三枚反足細胞於授精作用之後退化。胚珠或具多胚囊。胚乳發育的形式為核型。成熟種子只具胚而無胚乳。

Maackia taiwanensis Hoshei et Ohashi is an endemic species to Taiwan which belong to the Fabaceae, Faboideae. Trees are deciduous. Bisexual flowers are produced from early August to late August. The pods are maturing in December. Inflorescence primordia are formed at shoot apices in mid April. The primordia of calyx occur in late April. The primordial of petal, stamen and pistl occur successively from early June to late June. Calyx 5-lobed；petal 5, consisting of one standard, two wing and two keel-petal. Stamens 10, two whorls and anther are tetrasporangiate. The pistil is mono-carpellary with gynophore. Young anthers are composed of a protoderm and a central cell mass in early July. The anther wall layers consist of an epidermis, one layered endothecium, two middle layers and a tapetum of one layer. The development of anther wall layer belongs to the basic type. The tapetum is of the glandular type. Pollen mother cells undergo meioses through simultaneous cytokinesis and give rise to tetrads of microspores, which are tetrahedrally arranged. Mature pollen grains are 2-celled, globose, 3-colporate and 15~20μm in diameter. Anther dehiscence is longitudinal. The pistil with 2 to 5 ovules on a marginal placentation. Ovules are campylotropous, bitegamic. The outer integument is composed of 3 to 6 layers of cells in thickness, while the inner integument is of 2 layers of cells. The inner integument is degenerated during the seeds development. The megaspore mother cell is located 4-6 layers of cells beneath the epidermis at the nucellus top end. So it defined as crassinucellate. The megaspore mother cell divides transversally to form a linear megaspore tetrad. The megaspore at the chalazal end develops into the embryo sac mother cell. The development of embryo sac is Polygonum type. The two polar nuclei fuse before fertilization and the the three antipodal cells degenerate soon after fertilization. Multi-embryo sac might occasionally occur in an ovule. The endosperm deveolops through nuclei multiplication and is degenerated at seed maturing. Seeds consist of an embryo without endosperm.