ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 539 



thickness and becomes the middle lamella of the wall. In many cases 

 pcctose is also a constituent of the thickcniug-laycrs, so that the form 

 of the cell-wall is retained after destruction of the cellulose ; less often 

 the thickenings consist of pure cellulose. The walls of the tapetal cells 

 in youug anthers and those of young pollen-cells are composed, according 

 to the author, entirely of pcctose. Conversion into mucilage and cuticle 

 are results of the transformation of pcctose, not of cellulose. 



Permeability of Protoplasm for Urea.* — Herr H. de Vries states 

 that the protoplasm of mature cells can take up urea, Comjiaring the 

 rapidity of diffusion of urea with that of glycerin, he finds an illustration 

 of the general law that the diffusibility of a substance is in inverse pro- 

 portion to its molecular weight; that of glycerin CgHyOs (= 92) being 

 considerably less than that of urea CONaH^ (= CO). The isotonic 

 coefficient of urea he j)laces at 1 • 70. 



Diosmose through the Cellulose-pellicle of Phragmites communis.f 

 — According to Herren Kruticky and Bielkowsky, the cellulose-pellicle 

 of this grass has a greater endosmotic equivalent than that of any 

 artificial membranes hitherto used for the purpose. In the manometer 

 the endosmotic force withstands a pressure of nearly one atmosphere. 

 The limit of elasticity amounts, on the average, to above 500 gr. 



Reduction of Silver in the living-cell.$ — Prof. W. Pfeffer strongly 

 contests the assertion of Loew and Bokorny,§ that the reduction of 

 silver from a slightly alkaline solution is a conclusive proof of the 

 presence of "active albumin," and consequently of the cell being in 

 a living condition, which he asserts to rest on pure hypothesis. With 

 the death of the cell and its immediate result — the mixing of substances 

 previously separated, and the exosmotic separation of substances jire- 

 viously in contact — changes of various kinds are effected, of the chemical 

 nature of which we at present know very little. 



Messrs. Loew and Bokorny reply || to Dr. Pfeffer's objections, re- 

 ferring, in proof of the correctness of their conclusions, to the records 

 already published of their researches. In particular they assert that the 

 reduction of the silver-salt cannot be due to the presence of tannin, at 

 all events when this substance is not present in any large quantity. 



C2) Other Cell-contents (including' Secretions}. 



Chemistry of Chlorophyll.^ — Dr. E. Schunck gives a short resume of 

 the present state of our knowledge on the chemistry of chlorophyll, and 

 also adds a few new facts to the stock already accumulated. 



In works on vegetable physiology the term chlorophyll is sometimes 

 applied to the complex of substances contained in living green cells, 

 which take part in the process of assimilation, and of which the colouring 

 matter constitutes a portion ; and chemists, following the example of 

 physiologists in giving a name to the whole which should have been 

 confined to one part, have been led to ascribe to chlorophyll properties 

 which no mere chemical substance can possibly possess. The author 



* Bot. Ztg., xlvii. (1S89) pp. 309-15, 325-34. Cf. this Journal, 1888, p. 617. 

 t Arbeit. 8t. Petersburg. Naturf. Gesell., xix. (1888) p. 3. See Bot. Centralbl., 

 xxxviii. (1889) p. 486. 



t Flora, Ixxii. (1889) pp. 46-54. § Cf. this Journal, 1881, p. 906. 



II Bot. Centralbl., xxxviii. (1889) pp. 581-4, 612-5. 



i Ann. of Bot., iii. (1889) pp. 65-121 (1 pi.). Cf. this Journal, 1887, p. 606. 



