§2] UPON THE DIRECTION OF GROWTH 409 



injury to the greatly increased amount of ozone that appeared 

 in his vessels. In the open air, on the other hand, the increase 

 of ozone would be relatively so slight that it might well be 

 advantageous to growth. Warren's results would then be 

 accounted for by the fact that the ozone is especially produced 

 at the positive pole, thus favoring for a time the excessive 

 growth at that pole. On this explanation the electricity would 

 act only indirectly. Somewhat similar is the conclusion of 

 Thouvenii^" ('96), that the electric current aids the plant in its 

 decomposition of carbon dioxide. On the other hand there is 

 reason for believing that since plants are adjusted to an 

 (internal) electrical condition, a slight external one might 

 be advantageous rather than injurious. 



§ 2. Effect of Electricity upon the Direction of 

 Growth — Electrotropism 



In 1882 the Finnish botanist Elfving announced his dis- 

 covery that when the radicle of the seedling of a bean or of 

 certain other species was subjected in water to a transverse 

 current of electricity, it grew towards the anode. This was the 

 introduction to a series of interesting studies on what has been 

 ■called electrotropism. In classifying the data which have been 

 acquired we may make use of the following heads : 1. False 

 and True Electrotropism ; 2. Electrotropism in Phanerogams ; 

 3. Electrotropism in Other Organisms ; 4. Magnetropism ; and 

 5. Explanation of Electrotropism and Summary. 



1. False and True Electrotropism. — Elfving himself ob- 

 served two opposing phenomena in the seedlings which he 

 subjected to the current. In most cases the radicles grew 

 towards the anode, but in one species, Brassica oleracea — the 

 wild cabbage — the radicle grew towards the kathode. Elf- 

 VING was inclined, in consequence, to believe that some species 

 respond by growth in one direction and other species by the 

 opposite growth ; that these are diverse responses to the same 

 agent, just as negative and positive chemotropism are. Gradu- 

 ally, however, it became evident, chiefly through the work of 

 MiJLLER-HETTLnTGEx ('83) and especially Brtjnchorst ('84, 

 '89), that these results are due to dissimilar causes. Thus 



