This is where all the activity takes place on a growing saguaro cactus. The cactus grows upwards from this tip. While growing, it sorts out all the spines and extends the ribs. This is a very slow, but impressive, process. We have grown this particular saguaro since it was about 8 inches tall. It is now, about thirty years later, almost 5 feet tall. It doesn't appear that we will live long enough to see this one get arms or branches.