Figure 4. Apparatus for measuring P uptake. Roots caged in perforated capsules were added to bottles filled with ³²P-spiked calcium+MES buffer solution. Air bubbled through bottles insured adequate mixing. The solution is vacuumed out of the bottles after 10 minutes and bottles are flushed twice with unlabeled solution. Phosphorus uptake is calculated from the percentage of ³²P measured in the roots.