A less likely possibility, the extremely reduced form of autogamy [42 ], could not be completely discounted, because the second nuclear division (meiosis II) and subsequent fusion of haploid, sister nuclei might have been very rapid and thus the trinucleated stage (two sister nuclei following second meiosis plus a lasting pyknotic [homolog] product of the first division) in the young (small) auxospores difficult to capture.
Source: wiktionary