The Origin of spiral Growth in Phycomyces Sporangiophores

§ 1. Methods are described for the study of extension and rotation of sporangiophores of Phycomyces on varying the internal pressure and for determining the shrinkage on loss of natural turgor (fig. 3,4). The latter is about 2 atmospheres. Within this pressure range the stress-strain diagrams were determined (fig. 5). The distribution of extensibility in the growth zone is different from the distribution of growth rate, the zone of maximum extensibility being nearer to the sporangium than the zone of maximum growth rate, (fig. 8). The rotation per mm elongation with increased pressure is considerably lower than during growth (table 4) which shows that spiral growth must be due not only to the mechanical properties of the wall, but also to some special aspect of intussusception, (fig. ib). § 2. In mature cells and in cells where cessation of growth is induced by immersion in water, the wall becomes very rigid; its optical properties change and the direction of rotation with increased pressure is reversed. This is very probably due mostly to irreversible reversion of fibril orientation in the outermost layer of the primary wall. Reversal of orientation in certain layers of growing cell walls (not in such walls as a whole) is supposed also to be of importance in other cases. Reversed rotation also occurs when growth is resumed after the natural stagnation in growth in stages 2 and 3. This can be ascribed mainly to resumption of growth in areas where secondary wall material has already been laid down. § 3. Theories as to the cause of fibril orientation in the meristematic and secondary cell wall, in particular those on the origin of spiral structure, are considered and supplemented. It is a pleasure to thank Dr L. J. Audus for his correction of the English translation of this article.