Die Periodischen Bewegüngen der Blattorgane

Abstract

THE essential character of periodic movements as defined by Pfefifer is their being recurrent. All “repeated” movements, whatever their cause and mechanism may be, are periodic. Recurrent or periodic movements are of different kinds, and it is necessary carefully to distinguish between them. Thus certain periodic movements occur only during the growth of the part, and cease entirely when the structure has become full-grown; and the term “nutation” is restricted by Pfeffer to these recurrent movements during growth. In other cases periodic movements occur which are not determined by the growth of the part, but are due exclusively to the elongation and contraction of certain portions of tissue; and these latter are called by Pfeffer “movements of variation.” These movements of variation which occur so commonly in the Leguminosae are due to the action of more or less joint or hingelike portions of the leaf. Nutations on the other hand which occur in very many leaves or petioles are due to unequal growth of the tissues, and not to the presence of a joint. As the movements of nutation are dependent on the growth of the part, they cease when growth ceases; and as the zone of maximum growth of the part changes its position, so also the seat of the nutation will vary. The movements of variation have a very different character, as they continue when the leaf is full-grown, and naturally, as they depend on a definite structure having a fixed position, they do not change their place during growth. The two forms of movement are very closely related, and jointed parts during growth often exhibit movements of nutation, thus showing the close relationship that exists between the two. Die Periodischen Bewegungen der Blattorgane. Von Dr. W. Pfeffer, A.O., Professor in Bonn. Mit 4 lithographirten Tafeln und 9 Holzschnitten. (Leipzig: verlag von Wilhelm Engelmann, 1875. 8vo., 176 pp.) (The Periodic Movements of Leaf-organs. By Dr. W. Pfeffer, Extraordinary Professor in Bonn. With 4 lithographed plates and 9 woodcuts. Leipzig: W. Engelmann.)