水曲柳雌花发育、大孢子发生及胚胎发育的解剖学观察

Anatomic Observation on Female Flower Development,Megasporogenesis and Embryo Development of Fraxinus mandshurica

用石蜡切片法对水曲柳雌花发育、大孢子发生及胚胎发育的过程进行了解剖学观察。水曲柳在东北地区花期一般在5月,雌雄异株,雄蕊先熟,从散粉盛期到雌花开放间隔约一周,雌花一旦开放即可接受花粉。雌花雌蕊两侧具有退化雄蕊,子房2心皮2室,每室具2枚倒生胚珠,单珠被。薄珠心,单孢原,蓼型胚囊。大孢子四分体线形排列,通常合点端的1个大孢子为功能大孢子,但有极少数功能大孢子发生于合点端第2个或4分体两端的2个。核型胚乳。胚胎发育紫菀型,经历了合子、原胚、球形胚、心形胚和鱼雷形胚等不同阶段,6月末种胚形态分化完全,每子房中只有1个胚珠发育为成熟种子,种子单胚。对水曲柳典型的胚胎学特征和胚胎发生发育过程中的一些异常现象作了讨论。

The development of female flower, megasporegensis and the development of embryo of Fraxinus mandshurica were observed by the paraffin sectioning method. The tree species was dioecious and usually bloomed in May. Female flower bloomed about a week after pollen luxuriantly released. The stigma was receptive as soon as female flower opened. Female flower had two rudimental stamens beside its ovary. The ovary was twicarpellum, twilocular with two anatropous ovules each loculus. The ovule was unitegmic and tenuinucellar. The archesporium was unicelled. The development of embryo sac was of the Polygonum type. Four megaspores arranged linearly. Generally the megaspore of the chalaza was functional, while a few functional megaspores came from the second megaspore at the chalaza site or the two at the micropylar and chalaza sites. Endosperm was nuclear type. The embryogeny conformed to Asterad type, which passed through proembryo, heart, torpedo and cotyledonary stages. The embryo finished morphological differentiation in the end of June. Only one of the four young ovules developed to mature seed and every seed had one embryo in general. The typical embryological characteristics and some abnormal phenomena in embryogenesis of Fraxinus mandshurica were discussed.