§2] 



UPON THE DIRECTION OF GROWTH 



411 



T 



of the current.* DrrBois-REYMOis'D liad found that when a 

 current was passed through a cylinder of hard-boiled albumen 

 it became concave towards the anode owing to the passage of 

 water into the plant and its aggregation at the kathode side. 

 RiSCHAWi found that a cjdinder of plant tissue did the same, 

 and he attributed this result as well as that seen in the living 

 radicle to the accumulation of water at the kathode side. But, 

 as Brtjnchoest points out, this is not the whole explana- 

 tion, for the positive curving is generally accompanied by 

 death of the tissue, and death would not necessarily result from 

 the kathophoric action. By the use of a transverse partition of 

 porous clay Bruxchoest ('89) has been able to show that 

 the radicles in the positive 

 half of the vessel are much 

 more seriously affected than 

 those in the negative half, 

 which fact the kathophoric 

 theory will not explain, but 

 the chemical theory will (Fig. 

 117). In accordance with the 

 view that the positive reaction 

 is not a reaction to stimulus, 

 but is a false electrotropism, 

 it will be henceforth neg- 

 lected. The negative reaction, 

 on the contrary', is a response 

 to stimulus — a true electro- 

 tropism. 



2. Electrotropism in Phane- 

 rogams. — We have seen that 

 the transverse electric cur- 

 rent, when not too strong, 



causes a turning of the tip of the seedling from the anode. 

 That this turning is a growth phenomenon is indicated by the 

 fact that it takes place a few millimeters behind the tip in the 

 region of maximum growth. This is then the region of response. 



+ 



Mil 



Fig. 117. — Radicles of Phaseolus on opposite 

 sides of a partition, T, subjected to ■& 

 transverse electric current, of 6.5 5 inten- 

 sity, for two hours. On the positive side 

 of the partition all the roots are strongly 

 positive ; on the negative side, where the 

 water is being continually renewed, the 

 roots are slightly positive, being bent less 

 than 40°. (From Bkunchorst, '89.) 



* The kathophoric action is seen when an electric current passes perpendicu- 

 larly through a porous partition submerged in water. The liquid moves through 

 the partition towards the kathode (hence called also electrical endosmosis). 



