In Erigeron sumatrensis, Impatiens balsamina and Brassica campestris ssp. nipposinica, the percentage of the cathodic prophyll, calculated from a lot of lateral branches of the same genetic number, is more than seventy at the main part of the shoot, and it fluctuates weakly with the successive genetic number of the branch. It was proved by correlogram analysis that the percentage fluctuations of the cathodic prophyll on the successive branches are not a real random fluctuation, but are of a periodic nature in most cases. These facts suggest us that the prophyll position is determined by two kinds of factors, one of which, of course, induces the prophyll to occur mostly on the cathodic side and the other giving the periodic effect to the determination of the prophyll position.<br>In an erect shoot of Eurya japonica, which shows a spiral phyllotaxy, the variations of prophyll position are also periodic, when branches are traced in the genetic sequence. In this case the prophyll position seems to be determined by the periodic factor alone for the reason that both types of prophyll, the anodic and the cathodic, are found in the equal frequency on one shoot, contrary to the cases of the species mentioned above.<br>The period in successive variations of prophyll position was revealed by the correlogram as 2.62 nodes in the case of Erigeron. This value of the period corresponds just to one rotation of the phyllotactic spiral, then a definite phase of each period comes always on one lateral side of the shoot. This fact suggests that some environmental factors (e. g., sun-light effect) may induce the periodic variation of prophyll position. In the cases of Impatiens and Brassica, however, the period corresponds to more than one rotation of the phyllotactic spiral, so that the phase differences of the period occur on one lateral side of the shoot. In this case, it is not easy to look for any environmental factor which induces the periodic variations of prophyll position.