Early hypotheses

General dissatisfaction with chemical hypotheses

The Introduction to Part II lists the main hypotheses on phyllotaxis. Schwabe (1984) lists about 30 hypotheses. Steeves and Sussex (1989) give an account of the early hypotheses on phyllotaxis, such as Snow and Snow's (1931) first available space hypothesis elaborated from surgical experiments on Lupinus albus, Wardlaw's (1949a) physiological field hypothesis developed from experiments on Dryopteris (a fern) and originating in Schoute's (1913) work, and Plantefol's (1948, 1950) hypothesis of foliar helices.

Based on some of the assumptions regarding the mechanism at work in the complex apical area, numerous mathematical models were formulated in attempts to reproduce the various arrangements of shoot appendages. Successful reproductions of some types of spiral phyllotaxis were obtained, mostly for the types represented by the main sequence, and sometimes only by the first few terms of this sequence. The simulation generally instructs a computer to continue to reproduce a pattern already initiated by the modeler with a few primordia.

In Steeves and Sussex (1989) the field theory is presented as the most plausible hypothesis to explain the placement of leaf primordia in helical phyllotaxis. The fields are generally visualized in terms of the production of inhibiting substances or in terms of withdrawal of nutrients. Meicenheimer (1980) worked with Epilobium hirsutum in order to test his working hypothesis that auxin–induced growth–gradient interactions are the source of phyllotactic control in this species.