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The root surface area is important in planning treatment for restorative and preventive dentistry. Most of the methods presented in literature are based on membrane techniques using different materials. These methods become less accurate and cumbersome when root surface areas of multirooted teeth have to be measured. This report presents a method based on adsorption of benzene on plaster models of teeth to determine their surface areas.

Medicago introductions and an alfalfa cultivar were used to develop methods of screening for sources of alfalfa germ plasm resistant to root feeding by larvae of Sitona hispidula (F.). During the 3rd season of plant growth, cumulative feeding injury to tap roots was sufficient to permit evaluations of differences in number of feeding lesions and damaged root surface area. Percentage tap root surface area damaged was a positive linear function of the number of lesions at a near 1:1 ratio. Resistance or susceptibility can be evaluated best during the middle or end of the 3rd season of plant growth by making direct measurements of injury in 2.54-cm sections of the upper 15.24 cm of tap roots and using a maximum subsample of 24 plants/introduction.

SUMMARY The permeability to water of whole detopped root systems of five herbaceous species, all grown under the same conditions, was determined by the solution-change method of Arisz, Helder and van Nie (1951). Measurements of root dimensions allowed permeability to be expressed per unit of (a) root surface area, (b) endodermis area, (c) root volume, and (d) root length. By any of these four methods of calculation there were large differences in permeability between the species. Per unit surface area the permeabilities were: broad bean, 0·54; dwarf bean, 0·56; sunflower, 0·71; maize, 2·2; tomato, 6·1 nm second-1 bar-1. These differences cannot be explained by any obvious difference in root morphology. The permeability values fit with two previously proposed theories; (1) that much of the root resistance lies in the endodermis; and (2) that the resistance of the soil in the rhizosphere is small compared with that of the plant until the soil has dried to near or beyond the permanent wilting point.

Fluxes of Ca and P through intact corn roots growing in flowing, well stirred nutrient solutions, were determined. The flux of Ca increased linearily when the Ca concentration in the nutrient solution was raised up to 250 ppm Ca. An increase in the P concentration from 0.02 ppm to 0.4 ppm P resulted in a higher Ca flux at each Ca concentration. A P concentration of about 0.15 ppm was found to be the saturation concentration above which the P flux through the roots increased only slightly. A Ca concentration range of 100 to 200 ppm had no apparent effect on the P flux. The flux through a certain unit of root surface area for both Ca and P dropped to nearly zero after 150 hours of active absorption. It is suggested that this is connected with the decrease in the specific surface area of the root with age, which is proposed to be due to the suberization which was observed microscopically.

Nine rice varieties including three root types (I, II and III) were grown in both a nursery and a paddy field without transplanting. From both conditions samples were taken at their yellow maturation stages, in order to determine root ferrous coatings. The determinations were made by the o-phenanthroline method, after coatings were washed away by boiling the roots in IN-HCl for 45 minutes. From these experiments, it was found that the varieties belonging to the type I, of which root weight were larger than those of type II and III, were apt to have larger coatings per both plant and root (Fig. 1 & 2). As to ferrous coatings per unit surface area, it was nearly the same as those above mentioned (Fig. 3). Root surface area was calculated from root weight by such a formulae as A≒√^3(W proposed by the authors, in which A is the surface area and W is the weight per root. In addition to these experiments, seasonal changes of ferrous coatings were determined every 16 days after sowing, using three varieties of each root type. From these, it was found that, (1) ferrous coatings per unit surface area showed their maximum 44-60 days after seeding respectively according to varieties and then are gradually reduced till the period from heading to maturation (Fig. 6) and (2) those per plant and per root increased with the growth up to the maximum found at heading time (Fig. 4 & 5). These changes in coatings were also contrasted with the changes in the relative growth rates calculated by root weight increase. Maximum values in coatings were always observed at the periods when the growth rate dropped, that is, when the root activity lowered (Fig. 4, 5, 6 & 7).

A reliable method of measuring the root areas of extracted maxillary canines has been described. The mean root surface area of canines in males was found to be 2·63 cm. 2 and that for females 2·36 cm. 2 Assuming that a satisfactory force range for activating an orthodontic spring is 30–50 g. then the average force per unit root surface area would be between 11 and 21 g. per cm. 2 The wide variation in magnitude of root surface areas over the total sample suggests that it is impossible to describe precisely the applied orthodontic spring forces in terms of g. per cm. 2 root surface. These differences in root areas between individuals may help to explain the varying rates of tooth movement using similar spring forces.

(1963). Root Surface Measurement and A Method for X-Ray Determination of Root Surface Area. Acta Odontologica Scandinavica: Vol. 21, No. 1, pp. 35-46.