The origin and morphological evolution of th outer integument of angiosperms.

双被胚珠和倒生胚珠是被子植物中最常见和唯一的胚珠。利用扫描电镜对木兰目和樟目几个类群的外珠被进行了比较形态发生研究。旨在阐明被子植物外珠被的起源和形态演化。Winteraceae、Degeneriaceae、Eupomatiaceae、Atherospermataceae和Lactoridaceae的外珠被在珠柄的凹侧中断，然后变成帽状。而木兰科、丛梗藓科和三角木科则在珠柄凹侧的帽状外珠被的差距中插入珠柄突起。这一事实支持了一个假设，即内珠被起源于裸子植物起源时的端粒组装，外珠被起源于被子植物起源时的叶状器官。外珠被与舌蕨科和针茅科种子蕨的胚珠孢子叶进行了比较，结果表明：在鞭杉科和肉豆蔻科的半倒生胚珠中，珠柄凹侧的珠状突起形成得很早，以至于从表面上看不清楚帽状的外珠被。外珠被似乎是从一开始就开始倾斜的环状突起，这是由于帽状外珠被和索状突起之间的先天融合。Zippelia（Zippeliaceae，paleoherbal）的直生胚珠从一开始就表现为完整的杯状突起。没有迹象表明外珠被最初是兜帽状的。发育观察未发现杯状或斜环状外珠被是由兜状外珠被与珠柄凹侧的珠柄突起融合而形成的。

Bitegumic, as well as anatropous ovules are the most common in and unique to angiosperms. Comparative morphogenesis of the outer integument was performed in several taxa of Magnoliales and Laurales using scanning electron microscope. It aimed to clarify the origin and morphological evolution of the outer integument in the angiosperms. The outer integuments of Winteraceae, Degeneriaceae, Eupomatiaceae, Atherospermataceae, and Lactoridaceae arose as semi-annular outgrowth interrupted on the concaveside of the funiculus and then becomes hood-shaped. In Magnoliacea, Monimiaceae and Trimeniaceae, however, the funicular outgrowth intervenes in the gap of the hood-shaped outer integument on the concave side of the funiculus. This fact favors one hypothesis that the inner integument was derived from a telomic assembly at the origin of gymnosperms and the outer integument from a leaf-like organ at the origin of angiosperms. The outer integument is compared with the ovuliferous sporophylls of the glossopterid and caytonialean seed ferns.In case of semi-anatropous ovules of Himantandraceae and of Myristicaceae, the funicular outgrowth on the concave side of the funiculus was formed so early that the hood-shaped outer integument was not clearly seen from the surface. The outer integument appears to be initiated as on oblique ring-like outgrowth from the beginning as a result of congenital fusion between the hood-shaped outer integument and the funicular outgrowth. The orthotropous ovule of Zippelia (Piperaceae, paleoherb) was shown to arise as entire cup-shaped outgrowth from the beginning. There is no indication here that the outer integument is originally in hood-shaped. Developmental observation does not show the cup-shaped or oblique ring-shaped outer integument was formed as a result of ontogenetic fusion between the hood-shape outer integument and tha funicular outgrowth on the concave side of the funiculus.