Abstract: There is definitely seasonal activity in cambial growth in the trunk of Hevea brasi- liensis planted on Hainan Island and the cambial growth ceases during leaf-fail and leaf-absent period simultaneously with lower temperature and dries. The sieve elements founction for one-half year to two years. The variation in conducting-phloem thicknesses in a year is not significant and the conducting-phloem retains in about the same thickness during leaf-fall and leaf-absent period as that during the other periods in a year.

Key words: Hevea brasiliensis, Cambium, Phloem