Liquid-cultured primary roots of Yucca torreyi L. (Agavaceae), which are similar to its intact roots, develop uninterrupted files of calcium oxalate crystal idioblasts with raphide bundles in their cortex, beginning just proximal to the terminal meristem. Each single file of idioblasts displays a basipetal ontogenetic sequence. [1-14C]glycolic acid, [1-14C]glyoxylic acid, and L-[1-14C]ascorbic acid, all of which are potential precursors of oxalate, were each added to different flasks that contained a sterile liquid medium and isolated roots and were allowed to interact with the roots for 45 min. After thorough washing, the roots grew for periods that extended from 1.6 h to 24 h postincorporation before being fixed for light microscope autoradiography. Autoradiography of root sections with the L-[1-14C]ascorbic acid at the 1.6–6.0-h incorporation times showed concentrations of silver grains over the idioblasts, primarily over the vacuole crystal bundles and cytoplasmic plastids. The [1-14C]glyoxalic acid– and [1-14C]glycolic acid–labeled root sections showed a smaller amount of silver grains distributed over the entire sections, but these grains were not concentrated over the crystal idioblasts. These results strongly indicate that the L-[1-14C]ascorbic acid is the immediate precursor of oxalate in the crystal idioblasts of Y. torreyi primary roots and support more recent biochemical data regarding oxalate synthesis in higher plants. The use of roots in liquid culture containing uninterrupted files of developing crystal idioblasts could serve as a model system for additional biochemical, physiological, and molecular studies that seek to understand the formation and functional significance of crystal idioblasts in higher plant organs.