Growth model of Prototaxites according to Hueber (2001).
To the left in side view: the different stages are separated by blanks. The hymenium is always on the outside, followed by the sterile tissue.
Right below: the longitudinal section of the trunk: the black spots are the 'coltricioid clusters' of profusely branching generative hyphae.
On top right: half a transverse section of the trunk with growth increments and spots.