Excised mycorrhizas of Fagus were immersed in 35S solution for varying periods after which fungal mantles were dissected from host roots and both components were assayed separately for activity. In general 50% of the sulphur absorbed by mycorrhizas was found in the fungal mantle after 2 hours but this percentage was higher after shorter periods of immersion. Separation of mantle and cores before immersion in the active solution made little difference to absorption by either component.
A comparison was made between absorption of 32P and 35S in both excised and intact mycorrhizas. This showed that the two elements had different absorption patterns and it is concluded that the benefit due to possession of mycorrhizas lies in the large reservoir of phosphorus in the fungal component and in the increased rate of absorption of phosphorus even after this reservoir has been established.