Lichen Physiology

S ummary The main carbohydrates which incorporate 14 C during photosynthesis in Xanthoria aureola are ribitol, mannitol, arabitol and sucrose. Ribitol is the first product to accumulate 14 C in substantial amounts, and it appears to be produced by the alga. Ribitol is also the main form in which carbohydrate moves from alga to fungus. Entry of [ 14 C]ribitol into the fungus during photosynthesis could be prevented by addition of 1% 12 C‐pentitols to the medium. In short‐term photosynthesis experiments, incorporation of 14 C into mannitol is relatively small, and none is detectable in arahitol. However, in long‐term experiments, more 14 C eventually accumulates in mannitol than in other carbohydrates, and [ 14 C]arabitol can also be detected; the delay before appreciable accumulation of 14 C occurs into mannitol and arabitol is consistent with their being fungal products. Sucrose never incorporates much 14 C, but its early appearance in photosynthesis suggests it is an algal product. The rate of movement of a pulse of 14 C between the symbionts of X. aureola is much slower than in Peltigera polydactyla .