The vascular architecture of plants may constrain the pattern of resource movement among organs, resulting in morphological subunits that behave relatively autonomously, particularly with respect to carbon. Systematic and random patterns of leaf removal were imposed onCapsicum annuumplants to examine how architectural constraints may affect the development of sympodial branch systems. Removing leaves within a branch system resulted in a significant decrease in further sympodial growth by that branch, compared to a random pattern of leaf removal or to no removal at all. Data are consistent with the hypothesis that individual branch systems ofCapsicumfunction as integrated physiological units (IPUs). Developmental potential appears to be controlled within these IPUs.