The Uptake of Phosphate by Excised Mycorrhizal Roots of the Beech

S ummary Phosphate absorbed from KH 2 32 PO 4 solutions of low concentration by beech mycorrhizas is rapidly esterified. After periods of a few minutes about one‐half of that absorbed is found in organic compounds. Both fungal and host tissues when exposed, after separation, to radioactive phosphate solutions show this ability for rapid esterification. Whole mycorrhizas which had been allowed to absorb KH 2 32 PO 4 were rapidly dissected in the cold and the labelled phosphate fractions in their host and fungal tissues were separated. In the host tissue 90 % of the 32 P was found in inorganic phosphate after half a minute and this percentage fell to a little under 80 % after 10 minutes. The curve of percentage labelling of inorganic phosphate in the host tissue appeared to extrapolate to 100% at zero time. It is concluded that inorganic phosphate passes into the host from the fungus. This result is discussed in relation to previous work on phosphate absorption by mycorrhizas.