THE GROWTH OF THE CELL-WALL 33 



the nodes of grass-haulms, very thick-walled cells may remain capable 

 of growth. Indeed the protoplast may diminish or remove the mechanical 

 resistance to growth interposed by a thick cell-wall, either by dissolving 

 away several layers of the latter, or by softening the whole of it 1 . 



The properties of the cell-wall form only one of the factors concerned in 

 growth, and they can be locally or generally modified by the protoplast. Hence 

 the processes of growth will never be deduced from the character and molecular 

 structure of the cell-wall. The latter may still retain the power of growth when 

 impregnated with abundant deposits of prussian blue 2 or of silica s . Pronounced 

 impregnation with congo red 4 does, however, result in a cessation of growth, 

 but this may be due to a direct action upon the protoplast. 



By means of special processes of regulation a cell may attain any given 

 shape, although the cell-wall itself is equally capable of growth in all directions. 

 It is owing to this self-regulation that the cells of a Spirogyra filament never 

 exceed a certain diameter, although they remain meristematic. The same is the 

 case with the hyphae of fungi and of Vaucheria, in which the cell-wall ceases 

 to elongate immediately behind the parabolic growing apex 5 . The production 

 of lateral shoots in Cladophora and Caulerpa 6 shows that growth may be resumed 

 in localized regions of an adult cell-wall. 



The formation and growth of the cell-wall is the direct result of the activity 

 of the cytoplasm, but the interaction of the latter with the nucleus is also 

 essential. There is probably a certain advantage attained when this interaction 

 takes place across as short a distance as possible, but nevertheless the nucleus 

 does not always lie near to the region where the growth of the cell-wall is 

 most active. In fact, Townsend 7 has shown that very fine protoplasmic threads 

 suffice to maintain the necessary connexion. It is therefore uncertain whether 

 the common approximation of the nucleus towards the growing surface specially 

 favours the growth of the cell-wall, as Haberlandt 8 supposes, or whether it has 

 some other importance. It has, indeed, not yet been determined whether this 



1880, p. 8 (repr. from Sitzungsb. d. niederrhein. Ges.) ; Strasburger, Bau u. Wachsthum d. Zellhante, 

 1882, p. 189; Jahrb. f. wiss. Bot., 1898, Bd. xxxi, p. 588; Noll, Exp. Unters. ii. Wachsthum 

 d. Zellmembranen, 1887, p. 133; Klebs, I.e., p. 562 ; Zacharias, Jahrb. f. wiss. Bot., 1889, Bd. XX, 

 p. 113 ; Flora, 1891, p. 469, &c. On cuticle see Vol. I, Sect. 21. 



1 Pfeffer, Druck- u. Arbeitsleistungen, 1893, p. 401. 



2 Noll, 1. c., p. 132. 



3 Kohl, Kalksalze u. Kieselsaure i. d. Pflanze, 1889, p. 226. 



4 Klebs, Unters. a. d. Botan. Institut z. Tubingen, 1888, Bd. II, p. 515 ; Sokolowa, Wachsthum 

 d. Wurzelhaare n. Rhizoiden, 1897, p. 67. External agencies act usually by influencing the protoplast. 



5 On the path followed by the cellulose particles in the growing apex cf. Reinhardt, Jahrb. 

 f. wiss. Bot., 1892, Bd. xxn, p. 543. 



6 Nageli, Zeitschr. f. wiss. Bot. von Schleiden u. Nageli, 1846, Hefte 3-4, p. 82 ; Noll, I.e., 

 1887, p. 121 ; Klebs, I.e., p. 563 ; Zacharias, Flora, 1891, pp. 469, 482. The penetration of the 

 cuticle is also mentioned. 



7 Townsend, Jahrb. f. wiss. Bot., 1897, Bd. xxx, p. 484; Pfeffer, Sitzungsb. d. sachs. Ges. 

 d. Wiss., 1896, p. 509 ; Vgl. Bd. I, pp. 44, 482, 593. 



8 Haberlandt, Function u. Lage d. Zellkerns, 1887, p. 99; Sokolowa, Wachsthum der Wurzel- 

 haare u. Rhizoiden, 1897, p. 93; Miehe, Flora, 1901, p. 105. The nucleus always remains at the 

 bases of the root-hairs of Trianea bogotensis, although these grow at the apex only. 



PFEFFER. II D 



