234 A. B. Plowman — Electrotropism of Roots. 



half an hour by a current of *8 milli-ampere density. The side 

 of the root represented by the left-hand side of the figure was 

 directed toward the positive pole. Here the cells are evidently 

 in a state of partial collapse, the protoplasm is contracted, and" 

 the thin walls are more or less crushed. On the opposite side 

 of the root there is every indication of a perfectly normal con- 

 dition of the cells. Fig. 5 is from a longitudinal section of a 

 root of Hyacinilius orientalis, after three hours exposure to a 

 •7 milli-ampere current. This section is taken from a part of 

 root about M mm or 15 mra back of the tip, or at the point where 

 elongation was most rapid at the time when the current was 

 first turned on. It is perfectly evident that the cells on the 

 concave side of this root, or the side toward the positive pole, 

 were killed, while those on the opposite side kept on growing 

 quite normally. 



It should be mentioned in passing that when such curved 

 roots are fixed in Flemming's fluid there is always a conspicuous 

 white stripe down the concave side of the root, even after the 

 other parts have turned quite brown or even black. This is an 

 indication of the presence of dead cells in this region. The 

 same thing is often shown in roots while the electric current is 

 still acting upon them, by the fact that the concave side of the 

 root becomes translucent from the escape of cell-sap into the 

 intercellular spaces. 



The harmful effects of the current are even more strikingly 

 shown in cross-sections of the curved roots. Fig. 8 represents 

 a transverse section at 10 m,n from the tip of the root of Ilyacin- 

 thus oMentalis, after exposure to a *7 milli-ampere current for 

 one hour. Here the upper left-hand part of the section was 

 directed toward the positive pole. Fig. 9 is from a section of 

 such a root after two hours action of a similar current. In this 

 case the upper right-hand side was toward the positive pole. 

 Fig. 10 is an enlarged view of a part of the section shown in 

 fig. 9, along the line between the more affected and the less 

 affected parts. A comparison of these with fig. 6, taken from 

 a section of a normal root, shows that there has been more or 

 less shrinkage and collapse in all parts of the curved roots, but 

 that the actually destructive action has been confined to the 

 side toward the positive pole. This partial collapse of the 

 entire structure is not evident in a root exposed to a '1 milli- 

 ampere current, while a very brief action of a strong current 

 produces this effect in the entire root- tip, as shown in fig. 7, 

 which is from a section of a root of Hyacintlius orientalis, 

 treated for five minutes with a 10 milli-ampere current, 



From these facts of the minute anatomy of electrically curved 

 roots it seems to be self-evident that the curvature is the result 

 of the paralysis and death of the protoplasm on one side of the 

 structure, resulting in the complete arrest of development in 

 that region, while the other parts go on growing in a more or 



