Every Inch Protected
Not only in the form of cactus shown here, but in practically every form, the spines are so arranged as to protect every inch of the surface. It will be seen that it would scarcely be possible to touch a finger to the skin of the cactus plant above, so completely does the armor protect it. This form of cactus also gives an interesting illustration of the fact that away back in its history, the plant, instead of having flat slabs, had round stalks. In this picture the three joints of the round stalk can be clearly seen.
This image is from: Luther Burbank: his methods and discoveries and their practical application. Volume 1 Chapter 1