Unstable B-chromosomes in Ranunculus bulbosus

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 relatively high numbers (up to 19B) and are heterochromatic (visible in interphase nuclei after Feulgen or Giemsa staining procedures). In spite of the wide intra tissue range of B number the mitotic behaviour of B is very often regular. Also microsporogenesis observations have shown that Bs can pair and segregate regularly in the A chromosome fashion, especially when the B-number in meiocytes is low. Irregularities (clumps, laggards, micronuclei) ate much more frequent when Bs are more than six