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The suitability of stomata length as a criterion in the distinction between diploid and tetraploid rye-grass plants was tested.From the data it appears that diploid and tetraploid plants can be separated with a large degree of certainty if the selection is based on the stomata length .

Haploid plantlets from male fertile and male sterile sugarbeet plants could be induced at frequencies up to 2.2% using ovule culture. Ovary culture on media without charcoal resulted in a similar induction frequency. Plant development was inhibited by callus development originating from the mother tissue. When the callus parts were removed and the ovule transferred to a new medium without 2,4 D, callus formation could be inhibited by adding 0.5% charcoal to the medium. Up to 6.1% haploids were induced. Chromosome counts in leaf tips, chloroplast counts and isozyme patterns revealed that all plants were haploid and originated from the haploid cells of the embryo sac. Root tips showed spontaneous polyploidisation.

An autotetraploid population of caraway (Carurn carvi L.) was produced by treating the growing points of young plants with a 0.2% colchicine solution. Selection on morphology, pollen size and pollen shape, followed by a selection on seed size proved to be an effective way to identify the mixoploid C, plants. Three percent of the treated plants produced a tetraploid progeny. Moderate selection in the C, and the C, population resulted in an improvement of the average seed-set to the amount of 50% of the diploid control, with a range of 21-78%. The IOOO-kernel weight of the tetraploid material was 7 g, compared to 3 g in the diploid control. The oil content of the autotetraploid seed was increased with 35.6%; the increase in carvone amounted to 6.9%. The results of the experiment indicate that breeding work in autotetraploid caraway may result in a new cultivar.1NTRODUCTlON

In a collection of Poa pratensis the variation in chromosome number and the relation between chromosome number and plant characters were studied . The material was collected at different places in the Netherlands . The number of chromosomes in the population varied from 33 to 92 . Plants with 56, 63, 70 and 77 chromosomes were in the majority. The occurrence of different chromosome numbers within almost all investigated plants led to the conclusion that aneusomaty is a rule in Poa pratensis . In the progeny of some plants chromosome numbers were found which were considerably higher than those in the mother plants . It was assumed that this rise in chromosome number was caused by fertilization of aposporous egg cells . No relation could be found between chromosome number and plant characters . A hemiploid plant (39 chromosomes) was marked off from its sibs (77 chromosomes) by a stunted growth and pale leaf colour .