ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 243 



phyll-grains from the condition of apostrophe to that of epistrophe, the 

 epistrophic interval of the particular plant. 



The length of a plant's epistrophic interval depends upon the quality 

 of its protoplasm ; and it would appear that if an epistrophic interval 

 does not reach far to the right, it will extend some (perhaps all the) 

 way upon the left side of the photrum. In the case of aquatics, how- 

 ever, the epistrophic interval is developed far more upon the left than 

 upon the right side of the photrum. 



The author then discusses the nature of the movement of chlorophyll- 

 grains. The theory advanced may be shortly stated thus : — (1) Proto- 

 plasm is positively phototactic to light of medium intensity, and 

 negatively so to high grades of illumination and to darkness. (2) The 

 attracting and repelling actions of light impose a strain upon protoplasm. 

 (3) Lowering of the tone of protoplasm as respects light results from 

 withholding that agent. 



Mr. Moore has included in this paper a table containing all the 

 information he has been able to collect on what is called the " Law 

 of Positive Progression," which may be expressed in a general way by 

 saying that as an advance is made towards the positive end of the 

 photrum, the corresponding movement of the chlorophyll is performed 

 with more despatch, while the reverse is the case in proceeding towards 

 the negative end. Some points in the rotation of the protoplasm of 

 Elodea and Vallisneria are also touched upon ; and the author concludes 

 by giving the details of some experiments on the influence of light upon 

 rotation. 



Nuclear and Cell Division.* — Herr F. A. F. C. Went has examined 

 afresh several undecided points in the processes of the division of the 

 nucleus and of the cells. 



With regard to the nucleoli, he determined that, at least in many 

 cases, they are taken up into the nuclear threads on the commencement of 

 the division of the nucleus. As an object for observing this process, he 

 prefers the embryo-sac, especially of Monocotyledons, to pollen-mother- 

 cells. The staining material employed was safranin, either in alcoholic 

 or aqueous solution, and, for secondary staining, a mixture of diamond- 

 fuchsin and iodine-green in a solution of equal parts of alcohol and 

 water. 



By the use of fuming hydrochloric acid, a reagent which dissolves 

 chromatin, he also established the identity of the spindle-fibres and of 

 the ' ' combining-threads," the achromatic threads which unite the new 

 nuclei while in the course of formation. 



The author also describes the phenomena connected with the forma- 

 tion of the equatorial ring, which is accompanied by a shortening and 

 thickening of the spindle -fibres, drawing along with them the two 

 daughter-nuclei. This ring surrounds the cell-plate, and is distinguished 

 by its power of taking up safranin. 



Crystal-plastids.f — Under this name Herr A. Wigand describes 

 certain protoplasmic structures which he finds very widely distributed 

 within closed living tissue-cells, in root-hairs, aerial hairs, and in the 

 epidermis and parenchyma-cells. These structures appear to be 



* Bcr. Deutsch. Bot. Gesell., v. (1887) pp. 247-58 (1 pi.). 

 f Wigand's Bot. Hefte, ii. (1887) pp. 44-87. 



