(Photo 4)
Mammillaria luethyi
forma cristata
 a line crest completely defasciated

The defasciation is a process leading to longitudinal cleavage of a linear crest, rather to the complete division of the stem into individual normal shoots. Crests may remain at any stage for a long time. But at the stage of brain-shaped crest when the curves begin to crowd defasciation occurs rather often. That is the linear meristem turns into a number of small apical meristems that form normal shoots. More seldom defasciation occurs without any reason at an earlier stage of the development of the crest.

In general with age meristem gets less active or not active at all. The growth continues only at some parts of linear meristem. Thanks to this process the upper surface becomes uneven. The more active parts are usually situated at its ends. This type of developing crest prevails among cacti, and for a long time it was considered to be the only possible.