1881.] On some Effects of Transmitting Electric Currents. 151 



shorter. Inadequate currents, if directed downwards, produce nega- 

 tivity of the upper surface, which lasts for several seconds after the 

 current is broken. This effect is limited to the surfaces through which 

 the current is led. Its direction shows it is not dependent on polarisa- 

 tion. By opening induction currents, if their strength does not much 

 exceed the limit of adequacy, a leaf may be excited at intervals for 

 several hours without failure. Weaker currents are more effectual 

 when directed downwards than when directed upwards. If two inade- 

 quate induction currents follow one another at auy interval less than 

 0"*4 and greater than 0"*02, they may evoke a response. In this 

 case a response follows the second excitation. When a leaf is sub- 

 jected to a series of induction currents at short intervals (iV) * ne 

 response occurs after a greater or less number of excitations. If the 

 temperature is gradually diminished, the number is increased by each 

 diminution. All of the above statements relating to excitability refer 

 to plants kept in a moist atmosphere at 32 — 35° C. 



From the preceding facts, and others which are stated in the paper, 

 the author infers (1) that the " cross difference " is the expression of 

 electromotive forces which have their seat in the living protoplasm of the 

 parenchyma cells, and that it is due to the contact of cells in different 

 states of physiological activity ; (2) that the second phase of the 

 excitatory variation is probably dependent on the diminution of 

 turgor of the excited cells, and therefore on the migration of liquid ; 

 (3) but that no such explanation can possibly be accepted of the 

 phenomena of the first phase, the time relations of which, particularly 

 its sudden accession and rapid propagation, show it to be the 

 analogue of the "negative variation" or kt action current" of animal 

 physiology. 



II. " On some Effects of Transmitting j Electric Currents 

 through Magnetised Electrolytes." By Dr. G. Gore, 

 F.R.S. Received November 29, 1881. 



(Abstract.) 



This communication treats of a class of electro-magnetic rotations 

 observed and examined by the author. The rotations are produced in 

 liquids by means of axial electric currents, either in the interior of 

 vertical magnets, electro or permanent, or near the poles of such 

 magnets, and differ from rotations previously produced in liquids 

 placed in those positions, by the absence of radial currents, to the 



VOL. XXXIII. H 



