Die Sinnesorgane der Pflanzen

Abstract

THIS little book, which is appropriately dedicated to the memory of Darwin, was given as a lecture before the recent Versammlung deutscher Naturforscher und Aertzte at Breslau. The author devotes the chief part of his space to a semi-popular account of the various types of structures, such as bristles, hairs, papillæ, which serve for the perception of mechanical stimulus. This is necessarily, to a large extent, a recapitulation of his own interesting work on the subject, and is followed by an account of the statolith theory—the hypothesis independently put forward by himself and Němec as explaining the sensitiveness of plants to the force of gravity. The most interesting part of the lecture is, however, Haberlandt's concise discussion of his recent theory of the mechanism by which the direction of incident light is perceived by plants. He believes that the epidermic cells are, so to speak, the eyes of the plant. Thus, according to his view, when light strikes a leaf at right angles to the surface it results, from the plano-convex form of the epidermic cells, that the inner wall of each cell is illuminated more brightly in the centre than at the periphery. This makes it possible for the leaf to orientate itself in regard to light. Thus, suppose the plant to be moved so that the light now strikes the leaf obliquely, the bright patches of light on the inner cell walls will no longer be central. This change may be believed to constitute a stimulus calling forth a curvature of the leaf stalk by which the leaf is brought again to its normal position at right angles to the incident light. Thus the leaf moves when the bright patch is not central, and comes to rest when each of its epidermic cells is centrally illuminated. This attractive theory cannot be said to be as yet established, and botanists will look with interest to its further development by its author. The appendix of six pages is devoted to the literature of the subject and to short discussions of points which probably seemed too technical for the text of the lecture.

Die Sinnesorgane der Pflanzen.

By G. Haberlandt. Pp. 46. (Leipzig: Barth, 1904.) Price 1 mark.