THE ACTION ON VEGETATIVE GROWTH 119 



Plants differ greatly with regard to their power of developing upon 

 solutions of less or greater osmotic concentration. Thus many are unable 

 to grow upon solutions isosmotic with i to 2 per cent, sodium chloride, 

 or upon such solutions themselves, whereas many algae and fungi can grow 

 upon solutions containing 17 to 20 per cent, of salt, or isosmotic with these. 

 Hence certain organisms occur naturally in salt lakes whose water is 

 nearly saturated with salt, while a few small algae often appear in saturated 

 solutions of potassium nitrate. 



This power of accommodation is due either to the absorption of an 

 equivalent amount of salt, or to the production of osmotic substances by 

 metabolism until the original turgor is restored l . The requisite rise in the 

 concentration of the cell-sap is usually rapidly produced, but nevertheless 

 even then a sudden change of concentration produces a certain disturbance, 

 as is evidenced by the temporary retardation or cessation of growth 2 . This 

 result is produced by sudden decreases, as well as by sudden increases, 

 of concentration. In the second case transitory plasmolysis may take 

 place, whereas thin-walled cells may burst when organisms growing in con- 

 centrated solutions are suddenly placed in dilute ones 3 . This occurs when 

 Bryopsis or Derbcsia are placed in fresh water, whereas the marine algae of 

 estuaries are able to adapt themselves to daily changes from fresh to salt 

 water. Many plants which succumb to rapid changes can survive gradual 

 ones 4 , and Errera has shown that after continued cultivation on concen- 

 trated solutions the spores of Aspcrgillus nigcr acquire the power of 



1 See the works of Eschenhagen, Stange, Oltmanns, Richter, Bruhns, Fischer, Klebs, quoted in 

 Vol. I, p. 421. Also Errera, Bull. d. 1'Acad. royale d. Belgique, 1899, p. 95; Yasuda, Jour. Coll. 

 Sc. Imp. Univ. Tokyo, 1900, Vol. xm, p. 101 (flagellates, infusoria) ; Pettersson, Archiv I. Hygiene, 

 1900, Bd. xxxvn (bacteria). 



2 Stange, Bot. Ztg., 1892, p. 255 ; Richter, Flora, 1892, p. 55 ; Oltmanns, Jahrb. f. \vi-s. Bot., 

 1891, Bd. xxin, p. 370; Flora, 1895, p. 47; True, Annals of Botany, 1895, Vol. ix, p. 366. 



3 Cf. Eschenhagen, Einfluss von Losungen versch. Concentration auf Schimmelpilze, 18^9, p. 35 

 (fungi) ; Noll, Arb. d. Bot. Inst. in Wtirzburg, iSSS, Bd. Ill, p. 522 (algae) ; Lidforss, Jahrb. f. 

 wiss. Bot. 1899, Bd. xxxm, p. 247 (pollen) ; Fischer, Zeitschr. f. Hygiene u. Infectionskrank- 

 heiten, 1900, Bd. xxxv, p. i. Many pollen-tubes burst when they have attained a certain size 

 without the concentration of the external medium changing, and visible solid particles may even be 

 forced through the wall without any permanent pore being produced. Cf. Ewart, Trans. Liverpool 

 Biol. Soc., Vol. ix, 1895, p. 191. Fischer has observed a similar rupture (j>lasmoptyse) of bacteria 

 and also of infusoria (Jahrb. f. wiss. Bot., 1895, Bd. XXVII, p, 73) when transferred to concentrated 

 solutions. Fischer supposed this was due to the rapid penetration of the dissolved salt producing 

 an increased pressure inside the cell, but this is incorrect, for the most rapid diosmosis cannot do 

 more than equalize the pressures inside and outside the cell. If however growth were retarded while 

 the production of osmotic substances continued or increased, the pressure inside the cell might easily 

 rapidly surpass the elastic limit of the cell-wall, and so produce a mechanical rupture. The bursting of 

 pollen-tubes is probably produced in this manner. 



* Cf. Richter, Flora, 1892, p. 54 (algae); Stahl, Bot. Ztg., 1884, p. 166 (plasmodia); Karsten, 

 Diatom, d. Kieler Bucht, 1899, p. 152; Massart, Archiv. d. Biol., 1889, T. ix, p. 547 (bacteria); 

 A. Fischer, 1900, I.e. (bacteria). For instances of cells which cannot be plasmolysed see Pfefftr, 

 Pruck- n. Arbeitsleist., 1893, p. 307 ; Reinhardt, Botan. Festschrift fur Schwendener, 1899, p. 4:8. 



