Stem diameter appears to offer a convenient index of total plant leaf area during the period of grand growth for plants exhibiting apical dominance. In general this relationship appears exponential although cabbage exhibited a linear response. The measurements for cabbage were not continued into the stage of head formation, With the exception of one variety, differences between correlation coefficients or between M and N from the relationship A = MDN within varieties or between varieties of tobacco were not significant at the 5% level. Of 130 plants measured over 3 seasons only 3 plants deviated from the general mean at the 1 % level. Pooling across varieties of tobacco yields a respectable correlation which may be adequate for many purposes although the coefficient of variation is increased. Relationships determined for a single variety for two seasons did not show a measurable change. Our experience indicates that leaf area-stem diameter values for tobacco grown in a growth chamber do not apply exactly to field conditions or to different growth chamber environments (different light sources for example). Therefore it is recommended that a person using stem diameter as an index of total leaf area determine initial leaf area and final leaf area to check on the slope of the regression. Utilizing stem diameter as an index has led to the development of an electronic micrometer which allows the detection of short term responses of plants to changes in environment (Beeman, 1966; Splinter, 1967). This equipment is capable of detecting changes in stem diameter of 1.5 microns. Detection of changes in plant growth in a matter of minutes is thus possible. The utility of the stem diameter-leaf area relationships, along with electronic sensing devices should greatly improve the ability of plant scientists and engineers to study plant growth.

(Full article published with kind permission from "Tobacco International")