Chromosome number evolution in stem derived calluses ofHordeum vulgare L. culturedin vitro

Summary A study of the chromosome numbers of calluses obtained fromin vitro cultured stem nodes of barley over a period of time was carried out. The cells in division in the calluses were found only in growth centres (g.c.) which were independent of one another and easily isolated. At the beginning of the observations, the cell dividing population showed the diploid chromosome number. Tetraploid dividing cells appeared in the 5-month-old calluses and their frequency increased gradually. After 36 months of culture, the frequency of diploid and tetraploid cells was fixed at approximately 50%. The histological observation showed that in the 2-month-old cultures, the calluses were being formed from the epidermis as well as from the stem cortical parenchyma. The medullar parenchyma of the stem was not involved in the callus formation until 5 months of culture. Thus, it was possible to correlate the increase of the tetraploid dividing cell population with the formation of the calluses from the medullar parenchyma.