A survey of a number of species belonging to the Trifolieae has revealed that the first leaf in the mature embryo may occupy one of two positions, designated ‘inside’ and ‘outside’. Fourteen species exhibited an equal frequency distribution between the two classes, ten showed a bias towards an inside position, and two a bias towards an outside position. Complete determination was only encountered in other tribes of the Leguminosae.
In Trtgonella foenum-graecum L. the chance factor in the determmation of first leaf position acted independently in two adjacent ovules of a pod. Experiments demonstrated that the degree of inside bias of T. foenum-graecum could be influenced by nutritional and temperature treatments but not by light treatments. Supplementing plant cultures with manganese chloride solutions increased the bias, but calcium nitrate decreased the bias. Lower temperatures decreased the bias, and abolished it when plants were cultured at 15° C (day)/10° C (night).
Bias is an expression of genotype in offspring. By line breeding from two parent plants for three generations a hereditary component to the variability in bias could be shown to exist.
In Medicago rugosa Desr., which has an outside bias, manganese chloride as compared with calcium nitrate treatment favoured the inside position.
The view is advanced that the determination of a major morphological axis may come about as a consequence of random disturbances in a Turing type process.