ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 441 



during division. But, while chlorophyll-grains are simply bisected by 

 a central constriction, during the division of the nucleus a portion of 

 the parent-nucleus is not taken up into the daughter-nuclei, but is 

 absorbed into the cytoplasm. Only its framework passes entirely into 

 the daughter-nuclei, a portion of the matrix of the parent-nucleus does 

 not. The author also differs from Strasburger's view that the combining- 

 threads are partially identical with the spindle-fibres which originate 

 from the cytoplasm that penetrates into the nucleus. 



With regard to the formation of the cell- threads and cell-plate, the 

 author dissents from the conclusion of Berthold, and maintains that the 

 cell-threads originate in the barrel-shaped residue of the old nucleus 

 between the separated filameut-segmeDts ; the spindle-threads can still 

 be recognized in the residue. The nature of the cell-plate was made 

 out best in living rhizoids of Chara. The elements of the cell-plate 

 travel from the surrounding cytoplasm into the residue of the parent- 

 nucleus ; the longish bodies from which essentially the cell-plate is 

 constructed stand in no demonstrable relation to the fibres which are 

 visible in the homogeneous body after treatment with reagents. 



Zacharias identifies the process here described with the "perfect 

 karyokinesis " of Carnoy. 



With regard to the function of the cell-nucleus, the author was 

 unable to come to any definite conclusion. At least at certain times in 

 the life of the cell, when the nucleus is dividing, considerable quantities 

 of albumen pass out of it into the cytoplasm. 



To the above Herr G. Berthold replies,* maintaining the correctness 

 of his statements, in opposition to those of Zacharias. The coalescence 

 of the matrix of the old nucleus with the cytoplasm is very gradual, but 

 still is distinctly demonstrable. 



Herr Zacharias further replies f to several points in Schwarz's 

 rejoinder to the criticisms of Zacharias on his paper on the morpho- 

 logical and chemical composition of protoplasm. 



Structure and Growth of the Cell-wall. i — Herr G Krabbe has 

 investigated several points in the structure and mode of development of 

 the wall of cells, of which the following are the more important details : — 



With regard to the spiral striation of bast-fibres, the author agrees 

 with Dippel (in opposition to Xiigeli), that it is never the result of the 

 crossing of two systems in one plane. This is seen especially on trans- 

 verse section, where the striation-systems appear as radial lines, which 

 alter their position on a change in the focus. 



The mode of increase in thickness in the walls of bast-cells was 

 investigated especially in the Apocynaceae and Asclepiadeae. Krabbe 

 follows Strasburger in describing the wall as composed of distinct layers, 

 themselves made up of lamellae. The separate lamellae, "which are 

 especially distinguished by variations in the striation, arise by fresh 

 formations from the protoplasm, at first only loosely attached to the 

 older parts of the cell-wall, but always sharply separated from the 

 protoplasm, and showing distinct cellulose-reaction. It is probable that 

 the separate lamellae are all formed by new formation, and that increase 

 in thickness from intussusception can only play a subordinate part, and 

 must be confined to the innermost lamellae. 



* Bot. Ztg., xlvi. (1SSS) pp. 153-7. 



t Ibid., pp. 69-75, 90-2. Cf this Journal, ante, p. 69. 



X Pringsheim's Jalirb. f. WifiS. Bot., xviii. (1887) pp. 346-423 (5 pis.). 



