当小孢子从四分体中释放出来，特殊类型的外壁已经形成。
An extine with its specific pattern had already been formed, when microspores were released from tetrads.
外壁光滑。 周壁较厚，由周壁形成孢子的表面纹饰。
The exospore is smooth and the surface ornamentation is formed by the perispore.
细胞学观察和扫描电镜结果表明， 突变体花药发育过程中， 花药中小孢子外壁异常、破裂， 最后没有花粉形成。
The mutant has small siliques with no seed set. Cytological observation showed that during anther development, the microspores ruptured and no pollen grains formed in the mutant anther locules.
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