NOTES ON THE RESISTANCE AND STRATIFICATION OF THE EXINE

Partial decay of the exine in pollen grains of Epilobium and Geranium in mineral soils is described. An example is provided of exine corrosion, probably due to microbial activity, in birch pollen. Suggestions are made concerning “interbedded zones” in the nexine of Cobaea and Passiflora . Bacular conditions at or near the transition from the sexine to the nexine need more study. Cf. “stalactites”, “ordinary (infratectal) bacules”, and “quasi-ordinary bacules” provided (at least temporarily) with a distinct, root-like extension into the nexine etc. In conclusion it may be asked, if we - by altering, in one way or another, the “natural physiology of pollen development” - are able to get further insight into the mechanisms of still enigmatic morphogenetic etc. processes.