THE B-CHROMOSOME SYSTEM OF INNER MONGOLIAN AGROPYRON GAERTN .1. DISTRIBUTION, MORPHOLOGY AND CYTOLOGICAL BEHAVIOR

B chromosomes were found in varying frequencies in the diploid (56%) a nd tetraploid (5%) species in natural populations of Inner Mongolian A gropyron Gaertn., but there was no relationship between the presence o f Bs and the ecological and climatic conditions in which the populatio ns were found. Bs were usually smaller than As and showed polymorphism with three kinds of morphology: telocentric, metacentric and acrocent ric with this latter being by far the most frequent. The Bs showed gre at mitotic instability (from 0 to 6 Bs per cell) and they were present in pollen mother cells, in primary roots and in stem tissues, but not in adventitious roots. It was impossible to analyse their transmissio n through gametes. However, the meiotic behaviour of the Bs was regula r and similar to that of As. They paired between themselves as bivalen ts, multivalents up to pentavalents. Usually, they segregated normally and were rarely lost et AI and AII. The heterochromatic nature of Bs in Agropyron is discussed although heterochromatic bands were not obse rved following Giemsa banding techniques.