外壁外层——纹饰 sculpture 1L冒■ Tectum外壁外层—覆盖层 Pollen wall columellae柱状层 Foot Layer& Endexine外壁内层 ntine内壁 Pollen grain pe 3 Bi-cellular pollen grain外壁外层——覆盖层 外壁内层 内壁 柱状层 外壁外层——纹饰 sculpture Bi-cellular pollen grain