344 



LOCOMOTORY AND PROTOPLASMIC MOVEMENTS 



chemotactic they collect at the mouth of the tube, and in covered and 

 ringed preparations aerobic organisms will ascend the tube in search of 

 oxygen as the latter is exhausted outside (Fig. 61 C). If the organisms 

 are negatively chemotactic or are osmotactic they will collect at some 

 distance from the mouth of the capillary, and if they are positively chemo- 

 tactic to dilute solutions they will gradually approach the tube as the 

 substance diffuses from it. Convection currents due to differences of specific 

 gravity may be avoided by placing the tube open end upwards on the tilted 

 stage of the microscope T . 



Similar actions are exercised by the substances diffusing from a frag- 

 ment of solid, or from a piece of meat or the leg of a fly. In addition, 

 a drop of liquid may be tested in the manner shown in Fig. 60 2 . Plas- 

 modia may be grown on wet filter-paper having one end in water and the 



ABc 



(o) 



FlG. 61. Capillary tubes containing meat-extract and surrounded 

 by bacteria. A. showing attraction ; B, showing attraction exer- 

 cised by the air-bubble in the tube ; C, showing repulsion produced 

 by acidified meat-extract. (Magn.) 



FlG. 62. Drops of distilled water () 

 joined to drops of sea-water 10) containing 

 Spirillum forms. The latter collect where 

 the water is richest in salts, and hence ap- 

 pear to be repelled by the distilled water. 



other in the substance to be tested 3 . Currents of water must, however, be 

 avoided, since these may excite a rheotropic response. 



Antherozoids. The strongly chemotactic antherozoids of Ferns 4 

 escape in enormous numbers when small dry ripe prothallia are rapidly 

 washed and placed in a drop of water. They are strongly attracted to 

 a capillary containing o-oi per cent, of sodium malate, and a feeble 

 attraction is even exercised by solutions of o-ooi per cent, strength. Maleic 

 acid is much less attractive 5 , although more active and varied in its combin- 



1 Pfeffer, Ber. d. bot. Ges., 1883, p. 524; Unters. a. d. hot. Inst. zu Tubingen, 1884, Bd. I, 

 PP- 367, 45 1 ; ^SS, Bd. II, pp. 585, 627. 



2 Jennings, Journal of Physiology, 1897, Bd. xxi, p. 264; Massart, Bull, de 1'Acad. royale 

 de Belgique, 1891, 3 e ser., T. XXII, p. 152 ; Carrey, American Journal of Physiology, 1900, Vol. Ill, 

 p. 295. 



3 Stahl, Bot. Ztg., 1884, p. 156. 



4 Pfeffer, Ber. d. bot. Ges., 1883, p. 524; Unters. a. d. bot. Inst. zu Tubingen, 1884, Bd. r, 

 p. 367 ; Voegler, Bot. Ztg., 1891, p. 641 ; Buller, Annals of Botany, 1900, Vol. XIV, p. 543. 



6 Pfeffer,!. c., 1884. 



