3. Tetraploidy may be induced in the shoot apex of very young maize seedlings by introducing a dilute aqueous solution of colchicine through the cut end of the primary seminal root, or later in seedling development after the secondary seminal roots are established by introducing the colchicine solution through the base of the epicotyl following excision of the seed. Immersion alternately in .05% colchicine and water for 24-hour periods, usually for 4 days, effectively induced sizeable sectors of 4n tissue that persisted to maturity and affected both tassel and ear shoot. In some instances both ear shoot and tassel apparently were entirely tetraploid, and selfing such plants produced tetraploid seed. External applications of colchicine to ear-shoots and seedlings prove unsatisfactory as a practical method of chromosome doubling.

This seedling treatment technic is being adapted to the production of diploids from haploids in an attempt to obtain homozygous diploids from heterozygous maize stocks, especially commercial hybrids, in one generation.