Two points each. Ehleringer, et al.
Cactus stems possess areoles.
When a particular environmental factor is at its optimum, its relative effect upon cactus growth is assigned a value of 1.0. When a particular environmental factor is at its optimum, its relative effect upon cactus growth is assigned a value of 1.0. Environmental factors act in combination to determine overall cactus growth. In contrast, the majority of the stem cross section is yellow or yellow-white in color. Four points each.