There have been attempts to correlate stem structure with rooting ability of cuttings.

In particular, a continuous sclerenchyma ring of tissue in the cortex is typical in difficult-to-root mature phase cuttings.

Could this hard ring of tissue prevent roots from emerging from the stem?

Micrograph showing a stem cross-section with sclerenchyma ring identified.

Stem cross-section

Evidence suggests that this sclerenchyma ring is not the cause for lack of rooting in cuttings.

As observed with the cuttings to the right, the root primordia appear to have little trouble breaking through the sclerenchyma ring.

Micrograph of cutting with sclerenchyma and root primordia identified.

Adventitious root formation in eastern redbud (Cercis canadensis).