POISONOUS SUBSTANCES 77 



however, directly retard or inhibit streaming by increasing the viscosity of 

 the protoplasm and decreasing the amount of energy liberated, whereas the 

 acceleration is probably due to an indirect stimulating action. 



SECTION 33. Poisonous Substances. 



Acids. According to Dutrochet 1 , although dilute acids may cause 

 a temporary retardation of streaming in Chara, a complete stoppage is 

 always permanent, whereas with dilute alkalies a temporary stoppage 

 is readily produced. A temporary shock-stoppage may, however, be pro- 

 duced by suddenly immersing cells of Chara or Nitella in i to 2 per cent, 

 solutions of oxalic or tartaric acid for a period of a few seconds to a minute. 

 Recovery may occur on replacing in water. It is more difficult to do this 

 with physiologically equivalent solutions of nitric, sulphuric, and hydrochloric 

 acids (o-i to -3 per cent.), but occasional positive results show that the shock- 

 effect is actually due to the action of the acid, and not to any plasmolytic 

 effect. In Elodea, Vallisneria, and Tradescantia a temporary complete 

 stoppage can hardly ever be produced, although pronounced retardation 

 may occur without the power of recovery being lost. 



Both organic and inorganic acids exercise a very injurious effect upon 

 plant-cells 2 , chiefly owing to the readiness with which their hydrogen ions 

 are displaced by bases, and Klemm has shown that 0-05 per cent, solutions 

 of HC1, H 2 SO 4 , HNO 3 and H 3 PO 4 cause a rapid cessation of streaming 

 in hairs of Trianea, Momordica, Urtica> and cells of Vallisneria 3 . The 

 resistant power of different plants varies considerably ; thus many fungi and 

 the leaf-cells of Oxalis and of Crassulaceae, &c. are comparatively resistant 

 to organic acids such as oxalic, citric, malic, &c., while many fungi are also 

 resistant to mineral acids (HC1), though to a less degree. On the other 

 hand, Chara> Nitella and certain Bacteria appear to be less resistant 

 than any other plants as yet examined. Dutrochet (1. c.) found that 

 streaming ceased in Chara after fifty minutes' immersal in o-i per cent, 

 tartaric acid. Similarly, the addition of o-oi per cent, phosphoric acid 

 causes streaming in Chara and Nitella to undergo fluctuations of rapidity, 

 the periods of retardations becoming more and more marked until stream- 

 ing ceases in from half an hour to two hours. If the acid is washed away 

 just before streaming has ceased it may in some cases regain its normal 

 rapidity in a few minutes to an hour or so. Prolonged immersal in 

 o-ooi per cent, or even in large quantities of 0-0005 P er cent solutions of 

 this acid ultimately exercises a similar effect, provided the cells are free 

 from chalk. 



1 Ann. d. sci. nat., 1838, ii. ser., T. ix, p. 67. 



2 Cf. Fr. Schwarz, Cohn's Beitrage, Bd. v, chap, iv; Migula, Ueber den Einfluss von Saure- 

 losungen auf Algenzellen, Breslau, 1888. 



3 Klemm, Jahrb. f. wiss. Bot, 1895, Bd. xxvnr, p. 685. 



