Enige opmerkingen over de voortplantingswijze van Hieracium pilosella L. en enkele verwante taxa

In three species (Hauptarten sensu Zahn) of the subgenus Pilosella the following chromosome numbers were found: H. peleterianum (2n = 18), H. hoppeanum (2n = 18), and H. pilosella (2n = 18, 36, 45, 54, 63). Hybrids between H. hoppeanum and H. peleterianum on the one hand and H. pilosella (2n = 36) on the other, were triploid and completely sterile. The diploids and tetraploids proved to be amphimictic and selfincompatible. The higher polyploids turned out to be apomictic. In one case the pollination of a hexaploid plant with pollen of another hexaploid led, in addition to purely maternal sisterplants, to a single apomictic enneaploid (2n = 81). In another case the summation of the chromosomes of an unreduced egg cell of a heptaploid (2n = 63) plant and those of a reduced pollengrain (n = 27) of a hexaploid plant led to a single apomictic decaploid (2n = 90) plant. These high polyploids were not found in natural populations. Pollination of a sexual tetraploid plant with pollen of an apomictic hexaploid led to the formation of apomictic pentaploids.