Nobel P. S., Spine influences on PAR interception, stem temperature, and nocturnal acid accumulation by cacti, Plant, Cell & Environment, 1983, 6(2):153-159, doi: 10.1111/j.1365-3040.1983.tb01888.x
Experiments and modelling of the effects of spines on photosynthetically active radiation, temperature and nocturnal acid accumulation. In Cylindropuntia bigelovii, the relationship between physiological responses and light was compared with spines present and after their removal.