A previously proposed “canonical” model for the scaling relations among leaf, stem, and root biomass (ML, MS, and MR, respectively) asserts that the proportional relations ML ∝ MS3/4 ∝ MR3/4 and MS ∝ MR hold across seed plant species. This model is scrutinized by determining whether the scaling relations between ML, MS, and MR vs. basal stem diameter DS and between ML, MS, and MR vs. plant height h are logically consistent with previously predicted scaling exponents. For example, if ML is observed to scale as the 2‐power of DS and the model asserts that ML ∝ MS3/4, then MS must scale as the 8/3‐power of DS if the model is valid. Using a large data base for species with self‐supporting stems, statistical support was found for most such comparisons between predicted and observed scaling relationships. However, this judgement is predicated on (1) the assertion that the scaling exponents for MR with respect to DS (or h) are numerically “deflated” due to a systematic underestimate of fine and small root biomass and (2) the stringent protocol used to calculate the 95% confidence intervals of scaling exponents, which favors rejection of the model. In light of these features, the “canonical” model is logically consistent with the new scaling relations reported here. Therefore, the model is judged valid within the context of this evaluation.