Exine pattern determination in Angio sperm.

利用高分辨率扫描电子显微镜研究了外壁发育，注意保护层形成和组成的初始发育过程。保护层起源于四分体早期内陷质膜的突起部位。目前的研究表明，最初的保护层是由不规则取向的纤维丝。纤维丝在质膜上聚集并形成网络。在四分体阶段，球状物质逐渐聚集在纤维丝的网络内。随后，纤维线几乎被球状物质所掩盖。发育中的保护层在胼胝质四分体被膜内质地粗糙。游离小孢子时期，颗粒状的保护层变得均一。目前的研究表明，保护层由纤维丝和球状物质的协会。纤维丝可以作为受体和/或发育外壁的骨架。

Exine development was studied using high resolution scanning electron microscopy, with attention to the initial developmental process of protectum formation and composition. The protectum is originated on the protuberant sites of the invaginated plasma membrane during the early tetrad stage. The present study shows that the initial protectum is composed of irregularly oriented fibrous threads. The fibrous threads accumulate and form a network on the plasma membrane. Globular materials gradually aggregate within the network of fibrous threads during the tetrad stage. Subsequently the fibrous threads are almost masked by the globular materials. The developing protectum has a coarse texture within the callosic tetrad envelope. At the free microspore stage the granular protectum becomes homogeneous. The present study suggests that the protectum consists of an association of fibrous threads and globular material. The fibrous threads may function as receptors and/or the skeleton of the developing exine.