The possible causes of chromosome elimination included: (i) sudden shortage of proteins in developing embryo and endosperm, and (ii) the better ability of vulgare chromosomes, relative to bulbosum chromosomes, to forms spindle attachments. Other possible causes like differences inmitotic cycle, congression during mitosis, etc. were ruled out. It has also been demonstrated that the elimination of bulbosum chromosome is under genetic control. The use of primary trisomic and monotelotirsomics in crosses with tetraploid H. bulbosum suggested that both arms of chromosome 2 and the short arm of chromosome 3 of H. vulgare are responsible for chromosome elimination although their effect may be neutralized or offset if sufficient dose of bulbosum chromosomes is available. The effect of these vulgare chromosomes, however, will be indirect.