3. Dr. Sprague and I have begun some work on ultra-violet treatment of pollen, with the collaboration of Dr. F. S. Brackett of the Smithsonian Institution. The experiments haven't gone very far as yet, but it is clear that ultra-violet treatment of pollen induces genetic changes which show up as both whole endosperm and mosaic endosperm deficiencies at rates rather surprisingly high. A single progeny now growing in the greenhouse also shows about 10% of the plants with segregating pollen sterility. The results thus far therefore correspond to the changes to be expected from an X-ray treatment of pollen, with frequencies corresponding to a dosage of X-rays considerably lower than the maximum. Hovever, the doses of ultra-violet radiation used were also well below the maximum. Results from filtered and monochromatic ultra-violet radiations are not yet available.