Exine: Evolutionary Trends |
Evolutionary trends that became apparent when analysing the exine structures of angiosperms. The left part of the scheme shows cross-sections through different types of exines, that are displayed in top-view at the right. A further cellulose-containing layer, the intine that forms the layer below the exine in the pollen wall is not shown (J. W. WALKER, J. A. DOYLE, 1975).