Nobel P. S., Influences of Minimum Stem Temperatures on Ranges of Cacti in Southwestern United States and Central Chile, Oecologia, 1980, 47(1):10-15, doi: 10.1007/BF00541769
Measurements and a heat balance model relate stem structure, spines and hair covering to tissue temperature. The paper explains how plant temperature depends on the surroundings and the plant's own structure.