982 SUMMARY OF CUKRENT RESEARCHES RELATINQ TO 



In connection with tte relationship between swelling and double refrac- 

 tion, the author agrees with Zimmermann's statement * that all non- 

 cuticularized cell-walls show such optical properties as if they were 

 compressed in the direction of the strongest capacity for swelling, or with 

 that of the strongest shrinking when dried ; the strongest swelUng takes 

 place in the direction of the shortest axis of the ellipsoid of elasticity, the 

 least in that of the longest axis, and a medium degree of swelling in 

 that of the medium axis. This is shown in the cases of ordinary bast- 

 cells with longitudinal pores, of specific dynamic cells, of dynamic hairs 

 and pappus branches, of thick- walled cork-cells, and of Caulerpa. Molecular 

 tensions, such as those assumed by v. Hohnel, do not occur in any direction, 

 and the hypothesis that double refraction in starch-grains or cell-walls is 

 caused by such tensions must be abandoned. Such double refraction is 

 dependent on a different arrangement in different directions of the minutest 

 particles (molecules or micellae) of the substance. The author accepts, with 

 some limitation, Nageli's conclusion of the absence of optical susceptibility 

 of cell-walls to traction or pressure. This is especially true of normal 

 steroids. 



With regard to any change in the optical properties of the cell-wall 

 resulting from the imbibition of fluids, the author's experiments gave negative 

 results. 



Silicified Cells in Calathea.f — -Dr. H. Molisch describes peculiar cells 

 in the bracts of Calaihea Seemannii, surrounding the vascular bundles, 

 especially the bast-cells, completely filled by silica, or possibly by a 

 siKcate. They occur in such numbers as to form a complete coat of mail 

 around the vascular bundles. The walls of these cells are not silicified. 



C2) Other Cell-contents. 



Structure of Chlorophyll-graiiis.J — From an examination of the small 

 chlorophyll-grains containing very large " grana," in the creeping stem of 

 Goody era (Hsemaria) discolor, Herr V. Chmielewsky confirms Schimper's 

 and Meyer's hypothesis that the matrix (stroma) of the chloroplast is 

 colourless, the colour residing only in the vacuoles or " grana." 



He was also able to follow out accurately the development of the 

 starch-grains. As these are being formed the chlorophyll-grain gradually 

 increases in size, while its grana diminish ; and finally the entire chloro- 

 phyll-grain, with its grana, altogether disappears. In mature starch-grains 

 not the least protoplasmic remaias of the chlorophyll-grain can be detected. 

 The first layer of the starch-grain is formed on the periphery of the 

 chlorophyll-grain, from where it gradually extends to the interior. 



Hourly Variations in the Action of Clilorophyll.§ — M. J. Peyrou, 

 with the aid of a new instrument which he has lately had made, has investi- 

 gated the variations in the action of chlorophyll. He finds that the 

 function, at different hours of the day, is proportional to the intensity of 

 the light. His experiments were always made with an atmosphere saturated 

 with moisture in the case of terrestrial plants. Corresponding results were 

 obtained with aquatic plants. 



Starch-grains coloured red by Iodine. || — Herr A. Meyer replies to 

 Dafert's contribution on this subject, whom he charges with inaccuracy and 

 confusion on the chemic^i^side of the question. He epitomizes the 



* See this Journal, 1885, p. 476. 



t Verhandl. Zool.-Bot. Gesell. Wien, xxxvii. (1887) pp. 30-1. 



J Bot. CentralbL, xxxi. (1887) pp. 57-9 (1 pL). 



§ Comptes Eendus, cv. (1887) pp. 240-3, 385-8. 



II Ber. Deutsch. Bot. Gesell., v. (1887) pp. 171-81. Cf. this Journal, ante, p. 424. 



