FIG. 1.   Isotopic fractionation by three basidiomycete species grown under ambient atmosphere conditions in liquid cultures on either C₃- or C₄-derived sucrose. The species used were C. volvatus (Cv), M. androsaceus (Ma), and S. granulatus (Sg). Isotopic discrimination (_bf) was calculated from ¹³C values for the blank medium (Blank) and the total cell fungal biomass (cross-hatched bars). The standard error of the mean is also indicated for each bar. For each species, the solid bars represent the growth medium after fungal growth. The _bf values are significantly different from a hypothesized value of 0.00- for all C₃ treatments (t test; P < 0.001) and for C. volvatus (P = 0.04) and M. androsaccus (P = 0.007) on C₄ sucrose.