356 



LOCOMOTORY AND PROTOPLASMIC MOVEMENTS 



streaming as the result of shock l ; while, on the other hand, streaming 



may be excited or accelerated by a 

 diminution in the percentage of water 2 . 



TROPIC ACTIONS. A RHEOTACTIC 

 IRRITABILITY 3 has only hitherto been 

 detected in Myxomycetes, which creep on 

 wet filter-paper or other media against the 

 stream of water. To produce this move- 

 ment a slow stream is sufficient, as when 

 a plasmodium is developed upon a strip 

 of filter -paper placed with one end in 

 a beaker of water, and the other hanging 

 over the edge of the beaker. Since 

 freely motile organisms are carried along 

 mechanically even by a feeble current, it 

 is hardly likely that they should develop 

 any special rheotactic irritability. Hence 

 Roth's statement that certain Bacteria 

 do actually swim against currents of 

 water requires further proof 4 . 



HYDROTAXIS is also shown only by 

 the plasmodia of Myxomycetes 5 , and in 

 virtue of this irritability the plasmodium 

 creeps into a moist substratum. Towards 

 the time of fruiting, however, the positive 

 hydrotaxis becomes negative and the 

 plasmodium creeps on to the surface of 



the substratum, and up the developing sporangial stalks away from the 



moisture. 



FIG. 63. Cell from a staminal hair of Trade- 

 scantia virginica : A fresh in water, B the same 

 with ball and clumps of plasma c, in the zone 

 a-b exposed to induction - shocks. Magn. 400. 

 (After Kuhne.) 



1 Hofmeister, Pflanzenzelle, 1867, pp. 27, 53; Hermann, Studien ii. d. Protoplasmastromung bei 

 Characeen, 1898, p. 48 ; M. Tswett, Bot. Centralbl., 1897, Bd. LXXII, p. 329. 



8 Hauptfleisch, Jahrb. f. wiss. Bot., 1892, Bd. xxiv, p. 214. [The evidence as to any such 

 stimulating action of water on streaming is very unsatisfactory. On the physical action of the per- 

 centage of water cf. Ewart, 1. c., p. 12.] 



3 B. Jonsson, Ber. d. hot. Ges., 1883, p. 515 ; Stahl, Bot. Ztg., 1884, p. 147; J. B. Clifford, 

 Annals of Botany, 1897, Vol. xi, p. 180. According to Strasburger (Wirkung d. Lichts u. d. Warme 

 auf Schwarmsporen, 1878, p. 71) this action was first observed by Schleicher. 



* Roth, Centralbl. f. Bact., 1893, Bd. xin, p. 755. Aderhold (Jenaische Zeitschr. f. Naturwiss., 

 1888, N. F., Bd. XV, p. 314) could detect no rheotaxis in Euglena viridis. 



5 Stahl, 1. c., p. 149. Whether the Myxamoebae of Acrasieae (cf. Fayod, Bot. Ztg., 1883, p. 172 ; 

 Olive, Proceedings of the Boston Society of Natural History, 1902, Vol. xxx, p. 486), and also 

 Diatoms and Oscillarias, react hydrotropically is uncertain. 



