422 APPENDIX 



tion the organisms appear temporarily to be more sensitive to light, and show 

 a stronger tendency to negative phototaxis. 



Galvanotropism. Ewart and Bayliss (Proc. Royal Soc., 1905, Vol. LXXVII, B., 

 p. 63) have shown that the supposed positive parallelo-galvanotropism of roots does 

 not exist, and that this galvanogenic curvature is due to the stimulatory chemotropic 

 action of the products of electrolysis. When one electrode only is on the irritable 

 zone the curvature always takes place towards the stimulated side whether it becomes 

 acid or alkaline, but when a current of about o-oooooi of an ampere is led trans- 

 versely through the irritable zone the curvature takes place towards the acid side. 

 A similar curvature without injury is produced by the direct application of decinormal 

 acid and alkali on opposite sides of the root, and the application of an excised elec- 

 trolysed region of a root to another one produces in it a curvature towards the acid 

 side. Neither this ' positive ' curvature nor the ' negative ' one is traumatropic in 

 origin, since they are not necessarily accompanied by injury even to the superficial 

 tissues of the root. 



The negative curvatures are only shown when the direct action of the travelling 

 ions is not overpowered by the action of the accumulated products of electrolytic 

 decomposition in or around the root. If roots are imbedded in 3 per cent, gelatine, 

 in which the deficiency of oxygen almost entirely suppresses the geotropic 

 irritability, negative curvatures appear in the median region of the gelatine two or 

 more hours after passing through a four-volt current at right angles to the roots. 

 This is owing to the acid ions coming from the negative electrode exercising a 

 greater stimulating action than the alkaline ones repelled from the positive electrode. 

 Roots near to either electrode curve strongly towards them as the direct result of 

 the action of the accumulated acid and alkali at these points. Hence three 

 types of response are possible to the same current according to the position of the 

 roots, and all may be shown without injury. 



Transference of Stimuli. Kretschmar (Jahrb. f. wiss. Bot., 1904, Bd. xxxix, 

 p. 273) finds that an injury-stimulus causing streaming travels in the vascular bundles of 

 Vallisneria through distances of from 0-6 to 1-5 centimetres per minute, and more 

 rapidly towards older parts than acropetally. 



Phosphorescence. According to Molisch (Bot. Ztg., 1903, p. i), the best 

 luminous Bacterium is Micrococcus phosphoreus, which is readily obtained by laying 

 meat in 3 per cent, salt solution and keeping it moist at from 9 to 1 2 C. 



