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Theories concerning the causes of phyllotaxis may be divided conveniently into two groups. According to those of the first group, the arrangement of the leaves depends upon some unknown properties of the stem or the stem-apex. According to those of the second group, the positions in which the leaf-primordia arise are determined by the positions of the older primordia with which they make contact, or of any other members below them with which they may be in contact, such as cotyledons. Among the theories of the first group is that of SCHIMPER and BRAUN, who suggested that spiral sequences were due to a spiral growth impulse which travelled up the stem, the leaves arising at regular intervals along the course of this spiral

I. Experiments on Phyllotaxis. I. - The effect of isolating a Primordium