Abstract:Laticifer distribution and number were studied in diploid and tetraploid Euphorbia tirucalli L.. The laticifers are non-articulated. Primary laticifers are distributed mainly between the xylem and phloem and in the pith of 2-year-old stems as well. Secondary laticifers are scattered irregularly in the phloem, multi-branched. Terminal laticifers are present beneath the cortex (or periderm). Primary laticifers increase in number and size with stem growth. Then the diameter keeps a certain level and primary laticifers continuously increase in number to relief the sap pressure. Compared with diploid, the number of the primary laticifers decreased by 5.5 and 10.7 in newborn and 1-year-old stems of the tetraploid, respectively, and the diameter decreased by 5.5 and 8.4μｍ, respectively.