Empirical investigations into the tunica structuring point of the shoot apex of Pelargonium zonale.

A tunica structuring point of 3.85 cell units was formally predicted for the shoot apex. This point is decisive for the genesis of the tunica corpus structure as such and for the number of tunica layers in an apex at any given moment. Here, a method to determine, in empirical investigations, the theoretical number of tunica layers in real apices is demonstrated. Furthermore, results of an empirical investigation into the postulated tunica structuring point are presented and causes for deviations of the observed values from the theoretical values are discussed.