IRRITABILITY 239 



The net result of the many attempts to hasten the germi- 

 nation or to increase the germinating-power of seeds by 

 subjecting them to electrical action seems to be that there 

 are such great differences between plants of different species 

 ttat no general rule can be formulated.* Experiments on 

 the possible effects of the X or Rontgen rays upon the 

 growth of plants, from the pathogenic bacteria up, have 

 led mainly to negative results. 



It is claimed that the direction of growth is influenced 

 by electrical currents, that plants are galvanotropic or 

 electrotropic, positively or negatively, at least as to their 

 roots.t If Loeb's hypothesis (p. 238) be true that electri- 

 cal currents set up chemical changes in the cell, it would 

 be surprising if these produced no effect as shown by 

 the direction of growth. Still, the subject is far from ex- 

 hausted. 



Electrotaxis in plants is almost uninvestigated. Some 

 work on the movements of bacteria I with relation to electri- 

 cal currents has been done, but with meagre results. Zoo- 

 spores would suggest themselves as favorable objects of 

 study. 



INFLUENCE OF CONTACT 



By the term contact is implied much the same idea as is 

 expressed in the physiology of higher animals and in com- 

 mon parlance by the word touch. When the human finger 

 gently touches a motionless clean glass rod, the temperature 

 and other physical properties of which are similar to those 



* For description of method and the detail of beneficial effects of elec- 

 trical stimulation see Kinney, Electro-germination. Bull. Hatch Experi- 

 mental Station, Amherst, Mass., Jan., 1897, and Stone, Influence of 

 Electricity on plants. Bot. Gazette, vol. 27, 1899. 



f Elfving, F. tJber eine Wirkung dee galvanischen Stroms auf wachsende 

 Keimlinge. Botan. Zeitung, Bd. 40, 1882. Brunchorts, J. Uber Galvano- 

 tropismus. Ber. d. Deutsch. Bot. Ges., Bd. II., 1884, and Bot. Centralbl., 

 Bd. XXIII., 1885. 



X Verworn, M. Die polare Erregung der Protisten durch den galvani- 

 schen Strom. Arch. f. d. ges. Physiol., Bd. 46, 1890, p. 291. Lortet, L. 

 L'influenee dee courants induits sur 1' orientation des Bacteries vivantes. 

 Comptes Eendus de I'Acad. des Sciences Nat., Paris, T. CXXII., 1896, 



