Abstract:Chromosome numbers of 5 Zizyphus species are known. There is no odd ploidy, Zizyphussativa Gaertn. is diploid, and no spontaneous polyploid type has been found. The triploid plants were first induced from endosperm of Z. sativa in 1978. The endosperm-triploid began to blossom. and bear fruits in 1983. Its cytological behavior is as follows:1. The endosperm-diploidChromosome number of diploid is 2n = 24. Meiotic behavior is regular. At prophase Ⅰ and metaphase Ⅰ, 12 bivalents were observed. At the end of meiosis, normal tetrads occur, and the microspores are equal in size. The pollen grains are normal tricolporate ones.2. The endosperm-triploidChromosome number of triploid is 2n = 36. Its microsporocytes are larger than diploid. Meiotic behavior is very irregular. At prophase Ⅰ and metaphase Ⅰ, there are variable numbers of univalents, bivalents and multivalents, with the numbers of chromosome groups varying from 14 to 20. At anaphase Ⅰ, Ⅱ, disjunction is irregular, resulting in unequal chromosome numbers, lagging chromosomes, multipolar division and micronuclei. At the end of meiosis, some microsporocytes give rise to monads, diads, unequal tetrads, pentads and ha xads, and the microspores are not uniform in size. The normal pollen grains are larger than diploid, and are tricolporate or tetracolporate. Some small and aborted pollen grains were found.