On polyspermy in charlock ( Sinapis arvensis L.)

In previous experiments, the pollen of Helianthus L. was labelled with radioactive phosphorus. The measurements of the radioactive pollen and ovule samples were made with a Geiger‐Müller counter. The number of pollen contents per ovule was determined by dividing the radioactivity of the ovule sample by the radioactivity per pollen grain plus the number of ovules. This was possible since evidence was obtained that all radioactive phosphorus left the pollen grain and entered the ovule, and that the florets within the whorl are often equivalent. In the present experiments, polyspermy in charlock ( Sinapis arvensis L.) was studied. Flowers were pollinated with pollen from single stamens that were labelled with P‐32. The activity per pollen grain, as well as the activity per ovule (or seed), was determined by means of an anticoincidence arrangement for low‐level beta radiation. A high frequency of polyspermy, and of wide varying degree, was found in the experimental material. The highest number found was about 33 contents of pollen grains per ovule. With a certain significance, it was demonstrated that the values of the number of contents of pollen grains per ovule coincide with the uneven numbers and an interval of 4 in the integer series. The number of pollen contents per ovule is to a great extent dependent on the location of both the female and male flowers on the plant. The events comprising the fertilization process extended over a period of about 3 weeks. Some evidence was obtained that pollen grains showing high valency incorporate larger amounts of phosphorus.