Il Fusto Dell' Euonymus Alatus (Thunb.) Siebold Var. Typicus Regel E La Formazione Del Suo Sughero

Abstract

The stem of Euonymus alatus (Thunb.) Siebold var. typicus Regel and the formation of its cork. — Morphological and anatomo-histological research has been carried out on the stem of Euonymus alatus (Thunb.) Siebold var. typicus Regel taking in particular consideration the position and the structure of the corky wings typical of this species. These wings in number of two or four, opposite, lack in the area immediately below the points of attachment of the leaf and of the bud; but they appear further down in the basal part of the internode. It has also been observed that always in correspondence of this node, at 90[ddot] from the point of attachment of the leaf and of the bud, the two corky wings coming from the above internode descend with no interruption towards the following internode, and they stop at the point of attachment of the following leaf (figs. 1, 2). In correspondence of this node two other corky wings are found at 90[ddot] and their behaviour is exactly similar to the one already described. These corky wings originate through an active division of the epidermal cells confirming in this way the opinion of many authors, but not that of Kondratowicz (1950). The anatomical study has established that when there are four corky wings, a condition which occurs in quadrangular stems with four ridges, perfectly identical, in the woody ring, they originate in corrispondence of them. When the stem has two lateral expansion, due to the attachment of the two opposite leaves, to which correspond the two bigger ridges of the ring, the corky wings are two in number and they are placed in correspondence of the smaller ridges.

The mechanism which is responsible for the characteristics cross like disposition of the cork of this Euonymus might either consist in an increased tension in particular areas corresponding to the four woody ridges or it might involve an inhibition in the formation of the corky wings below the attachment of the leaf and of the bud, through the basipetal diffusion of a substance produced by leaves and buds.