UNSTABLE B-CHROMOSOMES IN RANUNCULUS-BULBOSUS L (RANUNCULACEAE)

A B-chromosome system has been found in Ranunculus bulbosus. 87 plants from Monte Croce della Serra in Umbria (Italy) have been examined and 12 of these have shown Bs. Bs in R. bulbosus are unstable (in roots, leaves and male meiocytes), very small (less than 1 mu m), can reach r elatively high numbers (up to 19B) and are heterochromatic (visible in interphase nuclei after Feulgen or Giemsa staining procedures). In sp ite of the wide intra tissue range of B number the mitotic behaviour o f B is very often regular. Also microsporogenesis observations have sh own that Bs can pair and segregate regularly in the A chromosome fashi on, especially when the B-number in meiocytes is low. Irregularities ( clumps, laggards, micronuclei) ate much more frequent when Bs are more than six.