To obtain a Cl-population with a high percentage of tetraploids after colchicine treatment of turnips, a selection in the C o can be used. A comparison is made between two criteria for this selection, viz. the average pollen grain size and the variation in pollen grain size.C0-selection on the basis of the average pollen grain size of five pollen grains per plant reduced the number of diploids in the C1 considerably. When the variation in pollen grain size of these five pollen grains is included as a selection-criterion the number of tetraploids in the C~ increased.The two methods are discussed in the light of the working efficiency and the genetical variation in the tetraploid C~-population. It is concluded that the character of the initial material should govern the choice of the selection criterion.
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