Abstract: The genus Malus Mill. of the Maloideae of the Rosaceae consists of about 35 recognized species, which are distributed in temperate region of the Northen Hemisphere including Asia,  Europe and North America.  Redher's classification divided the genus Malus into 6 series, 5 sections, of which 5 series, 3 section, including 27 species, occur in China. The chromosomal counts on 22 Chinese species were reported previously (Chen et al.,  1986; Liang,  1987). However, no comprehensive karyotype analyses have been made for most species reported. Analyzed in this paper are karyotypes of 36 forms, 22 species, and synapsis configuration of 6 polyploid forms in Chinese Malus to explore the relationships among species and provide cytological evidence for delimitation of species in Malus. Chromosome classification follows Li and Chen (1985). The materials used are listed in Table 1 and the vouchers are deposited in our depart- ment. The cytological results are shown as follows (see the data in Table 1, Plates 1-- 8 and Fig. 1). 1  Sect. Malus (1) Ser. 1 Baccata  The series consists of nine species endemic to China, 7 of which were cytologically observed: i.e. Malus baccata Borkh. 2n=34;  Sooo1-3 of M. baccata Borkh. 2n= 34;  M . mandshurica Kom. 2n= 34;  M. rockii Rehd. 2n=34; Sooo 3-2 of M.  rockii Rehd.  2n=51; M.  sikkimensis Koehne. 2n=34;  M. hupehensis Rehd.  2n=51; Sooo4-4 of M.  hupehensis Rehd. 2n=51;  M. halliana Koehne.  2n=34 and M.  xiaojinensis Cheng et Jiang 2n=68. The karyotypes consist of sm (8- 9  homologous chromosomes) and m (6- 7  homologous chromosomes)  as well  as st (1-2 homologous chromosomes). The chromosomes range in relative length from 9.84 to 3.74, with the ratio of the longest to the shortest from 2.28 to 2.03 and the mean ratio arms from 2.08 to 1.86. All the karyotypes belong to Stebbins's 3B except 2B of M.  Xiaojinensis.  Pollen  mother  cell (PMC)  of M.  hupehensis  contains 17I+17II, and the average synapsis configuration per cell is 2n=3x=51=17. 70I+ 15. 87II+ 0.52III, while PMC meiosis of M. xiaojinensis shows the synapsis configufations of 2n=4x= 68=4II+ 15IV. The latter has a remarkable and con- stant deleted chromosome, which is also the smallest in the karyotype.   (2) Ser. 2 Pumilae.  The series consists of six species endemic to China (Yu, 1979), all of which were cytologically examined, with the results: Sooo 9-8 of M. pumila Mill. 2n=34;  Sooo 9-12 of M. pumila Mill. 2n=34;  Sooo 9-7 of M.  sp.  2n=34; M.  asiatica Nakai.  2n=68; M.  prunifolia Borkh. 2n=34;  Soo 12-2 of M. prunifolia Borkh. 2n=34;  M. spectabilis Borkh. 2n=51;  M. micromalus Makino. 2n=34 and M. sieversii Roem. 2n=34. The karyotypes consist of sm(8-9 homologous chromosomes) and m (6- 7 homologous chromosomes) as well as st (1-2 homologous chromosomes). The chromosomes range in relative length from 10.77 to 3.42, with the ratios of the longest to the shortest from 2.95 to 2.04, and the mean arm ratios from 2.10 to 1.93. Therefore, all the karyotypes belong to 3B. Among more than 20 differ- ent forms of M. sieversii, there is only one ploidy level (2n=2x=34). PMC meiosis of M. spectabilis shows the synapsis configurations 2n=3x=51 =5I + 5II+ 12III.   2  Sect. II Sorbomalus   (3) Ser. 3 Sieboldianae.  This series has only one species endemic to China, M.  sieboldii  Rehd.:  One  triploid  from  Zunyi,  Guizhou  Province  has 2n=3x=51=24m+24sm+3st.  The  chromosomes  range  in  relative  length 8.74-- 4.17, with the ratio of the longest to the shortest 2.08, and the mean arm ratio 1.80. The karyotype, therfore, belongs to 2B. PMC meiosis of this form shows the synapsis conriguration 2n = 3x = 51 = 6I+ 9II+ 9III.   (4) Ser. 4 Kansuensis  consisting of four species endemic to China, 2 of which were cytologically studied, with the results: M.  toringoides Hughes. 2n=34, 51, 68 and M. transitoria Schneid. 2n=34, 51. The karyotypes consist of m (7—9  homologous  chromosomes)  and  sm (7—9  homologous chromosomes) as well as a few st chromosomes.  The chromosomes range in relative length from 9.44 to 4.01, with the ratios of the longest to the shortest from 2.26 to 1.83, and the mean arm ratios from 1.87 to 1.72. In M. toringoides four forms, 2x, 3x, 4x from Aba, and 3x from Barkang, in Sichuan Province, are of 2B karyotypes while 2x from Year zhu in Sichuan Province is of 2A. A mixploid with 3x, 4x in M. toringoides is found from Aba, with one smallest de- leted chromosome at both levels much like that in M.  xiaojinensis.  PMC meiosis  of  triploid  M.  toringoides  from  Barkang  showed  the  synapsis configurations of 10I+ 10II+ 7III. In M. transitoria 2x, 3x forms from Barkang, Sichuan Province and Lüda, Liaoning Province belong to 2A, while 2x, 3x forms from Aba, Sichuan Province both belong to 2B. PMC meiosis of triploid form from Lüda showed 9I+ 9II+ 8III synapsis configurations.   (5) Ser. 5 Yunnanensis  This series consists of four species endemic to China, 3  of which  were  cytologically  studied  with  the  results:  M.  ombrophila Hand-Mazz.  2n=34; M.  honanensis Rehd.  2n=34,  and M.  yunnanensis Schneid. 2n= 34. The karyotypes consist of nine pairs of m, seven pairs of sm and one pair of st chromosomes. The chromosomes range in relative length from 8.43 to 4.37, with the ratios of the longest to the shortest from 1.88 to 1.86, and the mean arm ratios from 1.75 to 1.72. Therefore, the karyotypes belong to 2A. Two pairs of heterozygous chromosomes, 1st and 10th, are found carrying a small satellite.