ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 653 



BOTANY. 



A. GENiERAL, including the Anatomy and Physiology 



of the Phanerogamia. 



o. Anatomy* 



(1) Cell-structure and Protoplasm. 



Formation and Growth of the Cell-wall.t — Herr E. ZacLarias has 

 investigated this subject in the case of the rhizoids of Cliara fcetida. 

 The membrane of the apex of the hair becomes considerably thickened 

 when the nodes on which the rhizoids grow are removed from the plant 

 and cultivated, the thickening becoming very considerable in the course 

 of a few hours. The first indication of this thickening is a layer of 

 minute granules which is deposited on the membrane of the apex of the 

 rhizoid ; the exact manner in which these granules are formed out of 

 the protojilasm is not clear; but in the course of a few minutes they 

 have formed themselves into a layer ot extremely delicate rods, placed 

 vertically to the membrane, which gradually become longer and tliicker, 

 and finally unite into a continuous layer of cell-wall. The chemical 

 reactions of the original granules could not be determined ; but the rods 

 very soon show a distinct cellulose reaction with chlor-zinc-iodide. 



It must be concluded fi'om the above that, in this case at all events, 

 the cell-wall increases in thickness by the deposition of a new formation 

 which is excreted from the protoplasm in the form of a layer of minute 

 granules, from which is developed a layer of rods manifesting the 

 reaction of cellulose. We have not here any direct transformation of a 

 peripheral layer of protoplasm into cellulose ; there is a much closer 

 resemblance to the new formation of a cell-wall in cell-division. The 

 young dividing-wall between two sister-cells of the rhizoids of Chara 

 consists in the same way of minute rods placed vertically to the growing 

 ■wall, which subsequently unite into a continuous layer. 



After its first formation the thickening-layer of Chara continues to 

 increase considerably in thickness ; but there is no further trace of any 

 new-formation, nor of an inner lamella differing in structure or reactions 

 from the rest of the thickening-layer. There is certainly here no 

 constant apposition of fresh layers of cellulose on the inner surface of 

 those previously in existence ; and in some rhizoids even the formation 

 of the primary layer, as above described, could not be detected. The 

 growth in thickness of the cell-wall therefore takes place either by intus- 

 susception or by the successive deposition of minute particles of cellulose 

 on the cell-wall. Whether the superficial growth takes j)lace by intus- 

 susception or by simple stretching could not be determined ; but the 

 facts seem rather to favour the first of these theories. 



(2) Other Cell-contents (including- Secretions). 

 Pure Chlorophyll.:}: — Herr A. Hansen gives a summary of the ex- 

 isting chlorophyll-literatm-e, now agrees with the view of Tschirch 



* This subdivision contains (1) Cell-structure and Protoplasm; (2) Other Cell- 

 conteuts (including Secretions) ; (3) Structure of Tissues ; and (4) Structure of 

 Organs. 



t Jahrb. f. Wiss. Bot. (Pringsheim), xx. (1889) pp. 107-32 (3 pis.); and Ber. 

 Deutsch. Bot. Gesell., vi. (1888) Gen.-Vers.-Heft, pp. Ixiii.-v. 



X ' Die Farbitoffe des Chloruphvlls,' 88 pp. and 2 pis., Darmstadt, 1889. See 

 Bot. Centralbl., xsxviii. (IS89) p. 662. 



