Dry peas were treated with solutions of 0.13% and 0.2% EMS for 24 hours at temperatures of 6°, 12°, 18° and 24°C, respectively. The effect of the temperature during treatment was studied in the M₁ and in the M₂ generation.

The germination capacity of the treated seeds and the percentage surviving M₁ plants were unfavourably affected only after treatment at 24°C. Leaf spotting and growth inhibition in the M₁ plants increased with increasing temperature, while fertility decreased. After treatment at 24°C more than 75% of the harvested M₁ plants were completely sterile.

With rising temperature the percentage mutants in the M₂ increased from 8 to 50%. However, the fertility of the mutants was considerably reduced. The sterility after treatment with EMS, therefore, must be at least partly due to genetic changes. This sterility greatly diminishes the mutagenic efficiency of EMS treatment at high temperatures.