IX. Experiments on Phyllotaxis. II. — The effect of displacing a primordium

Abstract
Part 1.— Introduction. (1) Nature and Purpose of the operations, and Methods. Experiments on Lupinusalhus were reported previously in which the arrangement of the subsequent leaves was changed as a result of the isolation from the stem apex of the region from which the next leaf or the next but one was due to arise (Snow and Sn o w , 1931). The results led to the conclusion that each new leaf-primordium arises in the first space that attains both a certain minimum width and a certain minimum distance below the apex (p. 36), a conclusion which strongly supports v a n It e r so n ’s theory of phyllotaxis (1907). The purpose of the present experiments was to test this conclusion further by means of a different operation performed on the same plant. The conclusion of the previous paper will therefore be taken again as a working hypothesis, and an attempt will be made to explain the present results on the basis of it. In the present experiments a slight vertical cut was made in a radial plane through the area from which the next primordium was due to arise, or in other words through the presumptive area of Ix (for terminology see section 4). The cut sometimes extended downwards a little way below this presumptive area, but probably never reached more than a very little above it. This operation was considered to be a suitable method for testing the conclusions reached previously for the following reasons. Firstly, if the centres of primordia arise only in positions that allow room for their stipules, as the previous results indicated (p. 23), any primordia arising in contact with the sides of the wound should arise with their centres at some distance from it, and consequently at some distance from the normal position of the centre of Ix. Secondly, as a result of these displacements, the positions of the subsequent primordia should also be changed, if they arise in accordance with the working hypothesis

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