SUPPLEMENT 83 



259, 11. 36-41, for It is a viscous . . . characteristic read It is a viscous fluid 

 whose external form, in the cases which interest us here, is determined by the 

 cell-wall. 



260, 11. 2-4, for In other cases . . . wall arises read The origin of the cell- 

 wall by excretion is extremely common, and only in a few cases has it been 

 definitely shown that it arises 



I. 9, for an extremely read a more 



II. 10-11, delete Cell-wall formation . . . protoplasm. 



11. 40-1, for the cell-wall . . . thickness read the cell increases in length, 

 but not in breadth. 



261, 11. 24-36, for Surface growth . . . solution of tannin, read The growth 

 in the cell has often been compared with the changes in shape observed in so- 

 called artificial cells. Such artificial cells (TRAUBE, 1867) may be readily 

 produced by taking a little gelatine, to which some sugar has been added, on the 

 tip of a glass rod, allowing it to dry, and submerging it in a weak solution of 

 tannin. 



1. 49, after offhand, read In the living cell, surface growth takes place only 

 in presence of protoplasm and nucleus, and, as a rule, such membranes grow 

 only when the protoplasm is closely applied to them ; this application is main- 

 tained firmly by osmotic pressure, while at the same time the cell-wall is stretched 

 by the same agency. 



262, 1. 41, after decreases, read This does not, however, appear to support 

 the idea of purely passive stretching. 



263, 1. 27 P. 264, 1. 41, for We may certainly . . . STRASBURGER (1889). 

 read In addition NOLL'S researches may be quoted, also the observations of 

 ZACHARIAS (1891) and of REINHARDT (1899). ZACHARIAS showed in the case 

 of the root-hairs of Chara, and REINHARDT in those of higher plants, that when 

 growth had been stopped by artificial means it was possible to cause a deposi- 

 tion of a distinct thickening layer at the apex of the root-hair, and that when 

 growth began again the older parts of the membrane which were incapable of 

 growth were burst by the younger ones, which had that power. Both authors 

 assume that in NOLL'S experiments the infiltration of prussian blue had induced 

 an inhibition of growth in the membrane, and that the bursting followed only 

 after that took place, and that when growth was uninterrupted, NOLL'S material 

 could not exhibit a formation of lamellae any more than those referred to. On 

 the other hand, NOLL believes that both in sections and in normally growing 

 organs, like in those studied by ZACHARIAS and REINHARDT, such structural 

 phenomena must be demonstrable. 



Assuming that apical growth takes place in general by deposit of lamellae, 

 that these grow and that the older ones burst, it doubtless follows that the 

 individual lamellae, at the moment when they are ruptured, would cease to 

 exhibit any surface growth, or at least would not grow as vigorously as the 

 young lamellae. The old lamellae would, doubtless, be stretched passively ; 

 whether, however, growth in the young lamellae is also passive, cannot be 

 decided from these experiments. Should it be the case that we have to deal in 

 these and similar instances, as also in the young membranes, with passive 

 stretching, one would naturally look to osmotic pressure as the active agency. 

 The fact, however, that this pressure is never sufficient of itself to stretch the 

 membrane passively is of great importance, for it has been shown that a pres- 

 sure even greater than it is incapable of extending the cell-wall beyond its 

 limits of elasticity (PFEFFER, 1892, 241). Further, we never find membranes 

 in the living cell which are stretched beyond these limits (comp. however, 



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