Fasciation and Dichotomy

1. The distinction made by Frank between fasciations, arising by gradual expansion of the vegetative cone in one diameter, and other malformations arising by connation of two or more separate stems or separate roots, is a natural one; N e s 11 e r’s proposal to restrict the use of the term fasciation to the former category has to be accepted. 2. Fasciation is due to a disharmonic growth, the central zones of the vegetative cone being dilatated by tangential growth °f the surrounding zone of differentiating organs. The cause of this disharmony is to be sought for in an excessive strength of the neutral central zone of the cone, which in its turn 15 the cause of an abnormally wide zone of organ induction, and consequently of a disproportionate number of organs (leaves and leaf-traces in the stem, vascular strands In the root). The gradual departure from the normal form of the organ, the pften occurring splitting, the increased number of leaves and the ’tregular phyllotaxis are all secondary consequences of the dilatation. 3- The tangential tension in the zone of differentiating organs usually gives rise to a transverse flattening of the vegetative cone; as soon as this occurs the dilatation henceforth acts in such a way that the elongation of the central zone is limited to the sagittal plane, giving rise to a typical fasciation. 4- In some cases the tangential growth of the differentiating organs causes a winkling of this zone; instead of a typical fas- ciation a radiate form ensues with otherwise the same characteristics. 5. In other cases the differentiating zone, being neither flattened nor wrinkled, dilatates the neutral part of the vegetative cone in an evenly distributed way; this leads to ring-fasciation by an exhaustion of the innermost part of the neutral zone in which consequently organs may be induced. 6. Connation of stems or of roots is due to confluence of the neutral zones of neighbouring vegetative cones during very young stages, in which no induction zones have been formed as yet by these cones. It is not accompanied by disharmonic growth phenomena. 7. Dichotomy is a spontaneous development of two centres in the neutral zone of a vegetative cone; the way in which this takes place is wholly unknown.