OSMOTIC AGENCIES 257 



Many plants are killed by a sudden change without any bursting or 

 plasmolysis. A slight change of concentration may injure or kill some 

 fresh-water algae 1 , and Stahl found that the plasmodium of Aethalium 

 septicum was partly or entirely killed when suddenly transferred to a 2 per 

 cent, solution of grape-sugar, or from this to a dilute nutrient solution 2 . 

 Many algae grow in estuaries, however, where twice daily they change from 

 fresh to salt water. Similarly the growth of mould-fungi is only tem- 

 porarily retarded by transference to nutrient solutions in which the increase 

 of concentration is equivalent to 4 per cent, sodium chloride. 



The cells of certain fungi, algae, and bacteria, as well as those of many 

 flowering plants, can withstand plasmolysis and resume their growth when 

 it is removed. Otherwise a new cell-wall may be formed around the 

 plasmolysed protoplast, which may remain living a few days or even a few 

 weeks, especially in a solution of sugar. The cells of other plants, such as 

 those of many species of Spirogyra^ die in a few hours when plasmolysed, 

 and all those cells are killed in which the most careful application of sugar 

 solutions produces either only partial plasmolysis, as in the cells of Chara 

 and Nitella 3 , or no plasmolysis at all, as in some primary meristems, and 

 in the hyphae of fungi 4 . 



All these results are produced by gradual increases of concentration 

 and when non-injurious substances are employed, so that they are due to 

 the purely physical osmotic action of the dissolved substance. The 

 injurious and fatal action is naturally accelerated by the use of poisonous 

 substances, and a feeble poisonous action is exercised by potassium nitrate, 

 sodium chloride, and other neutral salts of the alkalies, so that the 

 plasmolysed cells of mosses, algae, and flowering plants die in solutions of 

 these salts in a few days, although in isosmotic solutions of sugar they 

 may remain living for weeks 5 . Fungi and bacteria cease to grow in 

 solutions of potassium nitrate, sodium chloride, sugar, and glycerine of 

 approximately equivalent osmotic value 6 , although it has still to be deter- 



1 Richter, Flora, 1892, p. 54. Karsten (Die Diatomeen der Kieler Bucht, 1899, P X 5 2 ) finds 

 that many diatoms are rather sensitive. [It is only rarely that the change from fresh to fully salt 

 water is completed, and even then the change is gradual, extending over a period of two to six hours.] 



a Stahl, Bot. Ztg., 1884, p. 1 66. 3 Pfeffer, Jahrb. f. wiss. Bot., 1900, Bd. xxxv, p. 724. 



* Id., Druck- u. Arbeitsleistungen, 1893, p. 307 ; Reinhardt, Festschrift fur Schwendener, 

 1899, p. 425. 



5 Klebs, Unters. a. d. Bot. Inst. zu Tubingen, 1886, Bd. II, pp. 504, 548 ; de Vries, Mechanische 

 Ursachen d. Zellstreckung, 1877, p. 67; Pfeffer, Osmot. Unters., 1877, p. 134; True, Botanical 

 Gazette, 1898, Vol. xxvi, p. 413; Coupin, Rev. ge"n. d. Bot., 1898, T. X, p. 187; Ewart, 

 Protoplasmic Streaming, Clar. Press, 1903, p. 15. 



6 Cf. Eschenhagen, Einfluss von Losungen verschiedener Concentration auf Schimmelpilze, 

 1889, p. 55; Klebs, Bedingungen d. Fortpflanzung, 1896, p. 460; Massart, Arch. d. Biol., 

 1889, T. IX, p. 547. Fischer (Jahrb. f. wiss. Bot., 1895, Bd. xxvii, pp. 64, 153) finds that 

 ammonium chloride exerts a poisonous action on bacteria in comparison with sodium chloride and 

 potassium nitrate. 



PFEFFER. II C 



