DIFFUSE CHEMICAL ACTIONS 



343 



streaming in concentrations too dilute to cause a cessation of growth, 

 whereas in many cases the chemotactic or phototactic irritability is sup- 

 pressed before the power of movement l . 



Acids, even when in considerable dilution, such as from o-oi to 0-05 

 per cent, in the case of most 

 mineral acids, cause a rapid 

 cessation of streaming 2 . The 

 feebler organic acids are 

 naturally less effective, but 

 i-per-cent. solutions of tar- 

 taric acid produce a stoppage 

 of streaming within one or 

 more hours in all the plants 

 hitherto examined. Dutro- 

 chet 3 not only observed a 

 similar retarding action in the 

 case of alkalies, but also found 

 that the repeated change from 

 acid to alkali was more in- 

 jurious than remaining for the 



FlG. 60. Young root-hair of Trianea bogotensis. A before, 



Same length Of time in One an( l B one hour after, treatment with very dilute ammonia. (Magn. 



1000.) 



medium. Both acids and 



alkalies induce protoplasmic deformation, which is evidenced by the pro- 

 nounced vacuolation assumed as the result of treatment with alkali 4 

 (Fig. 60). Methyl violet, Bismarck brown 5 , as well as caffein and other 

 alkaloids 6 , may produce pronounced deformation without causing streaming 

 to cease. In all cases the timely removal of the reagent is followed by the 

 recovery of the protoplasm, which reassumes its normal configuration, but 

 poisonous reagents which combine with the protoplasm usually act fatally 

 before they can be removed. 



SECTION 74. Chemotaxis and Osmotaxis. 



The usual method of showing chemotaxis is to place a capillary tube 

 open at one end and containing a solution of the exciting substance in a drop 

 of liquid containing the motile organisms. If the latter are positively 



1 Rothert, Jahrb. f. wiss. Bot., 1903, Bd. xxxix, p. i, gives full details of actions of this character. 



2 Dutrochet, Ann. sci. nat., 1838, 2 e se"r., T. IX, p. 67 ; Klemm, Jahrb. f. wiss. Bot., 1895, Bd. 

 XXVIII, p. 685. 



3 Dutrochet, 1. c., p. 66: cf. also Ewart, 1. c., p. 80; Jurgensen, Studien d. physiol. Inst in 

 Breslau, 1861, Bd. I, p. 107. 



4 Klemm, 1. c., p. 658. 



5 Pfeffer, Unters. a. d. hot. Inst. zu Tubingen, 1886, Bd. II, pp. 250, 262, 264. 



6 Klemm, 1. c., p. 665. 



