The effects of conditioning temperature and length of the conditioning period on germination of seeds of the parasitic weed Orobanche crenata were investigated in vitro. Seed samples from Syria and Egypt, collected in various years, were compared. Optimum temperature for conditioning was 15–20 °C for Syrian seeds and 20 or 15–20 °C for Egyptian seeds. At 20 °C a conditioning period of 18 days was required for maximum germination. When conditioning at 20 °C was prolonged beyond 7 weeks, germination decreased. This effect was more pronounced for Egyptian seeds than for Syrian seeds. Germination of Syrian seeds was strongly reduced after conditioning for more than 4 weeks at 15 or 10 °C. A stepwise decrease in temperature during conditioning did not enhance this effect. The results of a tetrazolium test indicated that the seeds most probably did not die but developed secondary dormancy. Key words: Orobanche, germination, conditioning, temperature, dormancy.

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Spores of twenty species of Spirogyra were treated by acetolysis and viewed by scanning electron microscopy. The terms exo-, meso-and endospore should be maintained and based on chemical composition. Exo-and endospore are cellulose and/or pectin containing membranes. The mesospore is acetolysis-resistant and presumably contains sporopollenin.As basic pattern the spore wall in Spirogyra is composed of four layers: one exo-and endospore layer and two mesospore layers. The outer mesospore layer is mostly thin and hyaline, the inner layer thick and brown or yellow coloured and often sculptured. The germination suture is located in the inner mesospore layer. Some variations on this basic pattern were observed in Spirogyra bellis, S. cleveana and S. majuscula. Details of mesospore sculpture were observed and some taxonomic implications are discussed.The observed basic pattern is assumed to be valid for the Zygnemataceae as a whole.