[en] The role of cytogenetics in plant domestication is not as direct as that of plant breeding, agronomy or crop botany. Five major areas of cytogenetic interest in plant domestication are distinguished: analysis of the genetic structure of the species and its relation with other species, including genome analysis; monitoring of chromosomal, including meiotic, consequences of drastic genetic alterations such as artificial mutations (including somaclonal variation) and interspecific hybridization (including complete and partial protoplast fusion); induction, monitoring and adjustment of auto- and allopolyploidy; introduction of alien chromosome segments by meiotic manipulation and translocation; adjustment of the genetic transmission system, such as the construction of systems for hybrid varieties, allopolyploidization of (partial) autopolyploids or non-functional allopolyploids and permanent complex translocation heterozygotes. It is concluded that the last three areas are of interest only in the context of large programmes with sufficient and guaranteed input and continuity. (author). 23 refs

[en] The frequency of discolored sectors in the seedling leaves of Crotalaria intermedia is an index of two-hit radiation effects. Partitioning of an exposure to X-rays repeatedly results in frequencies lower than the sum of the frequencies induced by two single exposures ('below additivity'). When the first dose is small relative to the second, and the interval is sufficiently, but not excessively, long, a total effect significantly lower than that produced by the second exposure alone is observed. In the set-up used, changes in the composition of the cell population are improbable. It is suggested that this 'protection' is due to induced enzymic repair and/or protection systems which are liable to interfere with any interpretation of dose fractionation effects