Many Texas guayule plants examined cytologically at diakinesis and II prophase in PMC''s contained 36 to 39 chroms. (diploid number). Two dwarf plants had 36 to 38 chroms. Mere chrom. no. does not account fully for appearance and breeding behavior of guayule plants. The 36-chrom. plants may exist alone, or abundantly with a sparse 54-chrom. plant population or as off-types in a 72-chrom. population.