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

倒生胚珠和倒生胚珠是被子植物中最常见的，也是唯一的。用扫描电子显微镜对木兰目和劳拉目的几个分类群的外被进行了比较形态发生研究。本研究旨在阐明被子植物外被的起源和形态演化。冬青科、落新铁科、真珠母科、天精科和乳油科的外珠被呈半环状突起，在珠柄凹陷一侧中断，然后形成帽状。然而，在木兰科、莫尼科和三叉草科中，索状突起位于索状体凹侧的帽状外珠被的缝隙中。这一事实支持一种假设，即内珠被来自裸子植物起源的端粒组装，外珠被来自被子植物起源的叶状器官。外珠被与舌蕨科和肉豆蔻科种子蕨类的具胚珠的孢子叶相比较，半倒生胚珠在半倒生胚珠和肉豆蔻科的胚珠中，珠柄凹侧的珠状突起形成得太早，以至于从表面看不清楚帽状的外珠被。由于帽状外被与索状突起的先天融合，外珠被似乎从一开始就在斜环状突起上启动。胡椒属(胡椒科，古草本植物)的直生胚珠从一开始就是整个杯状的突起。这里没有迹象表明外珠被最初是帽状的。发育观察未发现杯状或斜环状的外珠被是帽状外珠被与索状突起在珠索凹侧的个体发育融合形成的。

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.