FORMATION AND MODIFICATION OF THE CELL- WALL 483 



It is doubtful whether the new wall formed around a naked protoplast 

 is produced by a metamorphosis of the outermost cctoplasmic layer, or by 

 the excretion of cellulose, or by both of these methods l . Carbohydrates are 

 often formed from proteids (Sect. 80), and direct researches with suitable 

 plants such as certain fungi may possibly show that changes and decomposi- 

 tions resulting in the production of cellulose may be induced by the 

 protoplast in the chitinous substances composing the enclosing cell-wall. On 

 the other hand, bearing in mind the marked secretory activity of which 

 protoplasts are capable, it is equally possible that the cellulose investment 

 may be produced by the excretion of preformed cellulose ; as a matter 

 of fact many of the Conjugatae, Flagellatae, &c. excrete a gelatinous 

 sheath 2 , which only needs condensation to become a more rigid cellulose- 

 wall. Cellulose is actually formed indeed from many mucilaginous sub- 

 stances when they are merely treated with acid 3 , protoplasts are able to 

 induce a variety of metamorphoses in the membranes enclosing them ; 

 while there is nothing to hinder the excretion and subsequent coalescence 

 of solid particles of cellulose. 



Nor is the mode of origin of the transverse walls in cell-division certain, 

 for although the cell-plate appears to be formed by the production and 

 aggregation of granules at a particular point 4 , it is not known whether these 

 granules unite directly to form the cell-wall, or whether, as often happens, 

 they are merely building material collected for further use, or again 

 whether they have a widely different functional importance. 



The co-operation of nucleus and cytoplasm is indispensable for the formation 

 and growth of the cell-wall, and when this condition is fulfilled cell-membranes 

 may be formed with considerable rapidity : thus a cell-wall appears around the 

 egg-cell of Fucus ten minutes after the entry of an antherozooid. A cell-wall may 

 appear around the plasmolyzed protoplasts of many plants in from fifteen minutes 

 to a few r hours 5 , for plasmolysis may excite to renewed activity a dormant power 

 of producing cellulose. 



Aerobes can construct cell-membranes only in the presence of free oxygen, 

 but obligate anaerobes have this power only when free oxygen is absent ; for this 

 and other reasons it is impossible to agree with Traube 6 in regarding the cell-wall 



Bd. XXXVII, p. 33), and also around certain vacuoles (Berthold, Protoplasmamechanik, iSS6, 

 pp. 296, 304). On cellulose granules, see Pringsheim, Ber. d. Bot. Ges., 1883, p. 288. 



1 No decisive experiments have as yet been made. Cf. Berthold, Protoplasmamechanik, 1886, 

 p. 154; Hofmeister, Zelle, 1867, p. 147. 



2 Klebs, Unters. a. d. Bot. Inst. z. Tubingen, 1886, Bd. II, p. 411. 



3 Cf. Tollens, Handb. d. Kohlenhydrate, 1888, Bd. I, p. 220. 



4 Cf. Zimmermann, Morph. u. Physiol. d. Zellkernes, 1896, p. 72. 



5 Hofmeister, Zelle, 1867, p. 151. Townsend, Jahrb. f. wiss. Bot., 1897, Bd. xxx, p. 484 ; Stras- 

 burger, Studien liber Protoplasma, 1876, p. 54. [Farmer and Williams, Observations on the Cytology 

 and Fertilization of Fucaceae, Phil. Trans. 1898, p. 625.] 



" Traube, Monatsb. d. Berl. Akarl., 1859, p. 83. 



I i 2 



