ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 65 



Course of Molecular Physiology.*— H. Schoufceden has edited the 

 manuscript of a course of lectures by the late Professor Leo Errera on 

 the application of physical laws to the phenomena of plant physiology. 



Irritability. 



Geotropism in the Roots of Lupinus albus.f — P. M. G-eorgevitch 

 has made a cytological study of the roots of Lupinus albus with special 

 reference to geotropism. The root-cap surrounds a columella, which, 

 together with the adjacent cells, is rich in starch-granules. Normally 

 these granules rest upon the physically lower cell-walls. In the normal 

 cells of the root-tip the nucleus behaves as if lighter than the rest of 

 the cell-contents, while the starch-corpuscles appear to be heavier, and 

 follow the direction of the force of gravity, when the position of the 

 root is changed. There is in each cell an accumulation of protoplasm, 

 which stains very deeply, and which bears an important relationship to 

 the position of the starch-granules, for when the root-tip is bent, so 

 that gravity acts at right angles, or parallel to the organic axis, the 

 starch-granules cover the physically lower cell-wall, while the proto- 

 plasmic layer rests upon the morphological lower cell-wall. The move- 

 ment in any direction of the starch-granules is always accompanied by 

 movement of the protoplasmic layer. Also, the cell-nucleus is influ- 

 enced by the force of gravity, and can be either positively or negatively 

 geotropic. The cell-nucleus of geotropically directed roots shows the 

 same structure as that of the ordinary cell-nucleus, and exhibits normal, 

 mitotic cell-division. The cells of the growing root under the influence 

 of gravity behave as if subjected to a one-sided pull or pressure, those 

 on the concave side being short and broad, while those on the convex 

 side are much elongated. 



Epidermis of Foliage-leaves in Relation to Light-perception. $ — 

 M. Nordhausen has experimented with Fittonia, Impatiens, etc., with 

 special reference to the connection of the epidermal cells with light- 

 perception. Haberlandt's theory that the papillose outer walls of the 

 epidermis act like lenses, throwing light upon the opposite sides of the 

 cells, the plasmic linings of which are sensitive to light, has not been 

 confirmed by the present experiments. Moreover, the reason put forward 

 by Haberlandt for the failure of certain experiments, viz. that the light- 

 sensitiveness is not inherited but acquired, and may, therefore, vary 

 with changed conditions, is criticised by the author, who contends that 

 this sensitiveness would then be constantly changing under normal 

 conditions. The conclusion appears to be that the papilla? of the epi- 

 dermis stand in no direct causal relationship to the perception of light 

 by the leaf -blade. 



* Cours de Physiologie Moleculaire fait au doctorat en sciences botauiques en 

 1903 par Leo Errera. Extrait du Recueil de l'lnstitut botanique de Bruxelles, 

 VII. Brussels: Lamertin, 1907, xii. and 153 pp., 20 figs, in text. 



t Bot. Centralbl., xxii. (1907) pp. 1-20 (1 pi.). 



X Bot. Gesell., xxv. (1907) pp. 398-410. 



Feb. 19th, 1908 f 



