Changes in sizes and shapes of sex organs - antheridia and oogonia - were studied in wild populations of Chara vulgaris collected during summer, autumn, and from samples cultured in the laboratory under varying L:D and temperature conditions. Morphometric measurements indicate that the size variations refer mainly to male sex organs, while those evidenced for oogonia are much lower. Our observations are discussed in terms of changing morphogenetic preferences for antheridia and oogonia within the life-span of a plant.