Page:The Journal of Indian Botany.djvu/408

354 THE JOURNAL OF INDIAN BOTANY. Small, James " The Chemical Reversal of Geotropic Response in Roots and Stems" — The following abstract of a paver read before the Linnean Society, March IS, 1920, is taken from the minutes of the meeting.

When roots are placed horizontally in a moist atmosphere rendered very faintly alkaline by ammonia vapour they tend to grow upwards. When stems are treated in a similar way with acetic acid vapour they tend to grow down- wards.

These experiments, illustrated by photographic lantern-slides, form preli- minary confirmation of the following theory of geotropic curvature, which has been elaborated as a co-relation of previous work on the electrical con- ductivity of roots with data accumulated by other investigators.

The outer zone of the protoplasm in the cells of the apical meristem is an emulsion with a continuous phase of colloidal aqueous solution and a disperse phase of protein or protein-lipoid particles, which show Brownian movement and carry an electropositive charge when the hydrion concentration of the continuous phase is higher than the isoelectric point of the vegetable proteins, or an electornegative charge when that hydrion concentenation is lower than the isoelectric point of the proteins. The continuous phase or medium in the root is relatively acid and that in the stem is relatively alkaline.

Creaming of the emulsion under the influence of gravity causes differen- ces of potential in the apex of root and stem, which produce electric currents. These produce differences in permeability, turgor, and rate of growth. The direction of these currents is determined by the positive charge in the root and the negative charge in the stem with corresponding downward or upward curvature.

The reversal of curvature in the experiments is due to the reversal of the electrical charges on the particles of the disperse phase, which is caused by the changes in the relation of the hydrion concentrations to the isoelectric point of the proteins. This theory explains practically all the details of known geotropic phenomena, including the orientation of the secondary and tertiary branches of roots and stems. It has very wide applications to cyto- lysis, the stimulus response ratio of the Weber Law, acid-tolerant and calci- fuge species, immunity from and liability to attack by bacteria and fungi, the development of intumescences, the effects of acids, alkalies, and salts on plants and animals in general and on the permeability of protoplasm in parti- cular, and possibly also to epharmonic variations. It provides on explana- tion, not only for the normal polarity of growth in the plant, but also for the changes in geotropic response and in colour which occur in flower-buds and other organs.

Indications have been obtained that the Co 2 balance in stem and root is the chief factor governing the differentiation in hydrion concentration, and also that phyllotaxis can be explained in terms of the potential differences postulated.

White, Orland E. Breeding new castor beans. Jour. Heredity 195—200- 5 figs. 1918. The author calls attention to the desirability of developing improved