li)04.] PUBLIC DOCl'MKNT — No. 33. 29 



There is a niiniuium, optiiuum and niaxiinum current 



which ogives rise to reactions similar to those obtained from 



o 



other iornis of stimiih. There is also a well-defined latent 

 l)eriod, such as we find associated with heli()tr()i)ic and geo- 

 tropic stimuli, etc. Moreover, there exists a definite relation- 

 ship between current intensity and perception, or reaction 

 of the organism, as in chemotactic stinuilation. 



It was observed by early experimenters that there existed 

 a dift'erence in the growth of plants when su]))ected to what is 

 termed positive and negative charges. Oui" limited experi- 

 ments in this respect have shown tliat when seeds were treated 

 with a positive charge the growth of the ro(jts was greatly 

 accelerated, while the stems were nmch less so ; and con- 

 versel}^ Avhen treated with a negative charge, the stem 

 showed a greater accelerated growth than the ro{)ts. Ger- 

 mination — that is, radical development — was greatly accel- 

 erated when seeds were charged positively, although when 

 charged with a negative charge germination at first was much 

 less accelerated than in untreated seed. Thus we have a 

 positive charge stinmlating organs which react in a positive 

 manner, and a negative charge stimulating organs which 

 react in a negative manner ; also the eftect of a positive 

 charo-e actino- as a sli":ht stimulus or retarding organs which 

 act in a negative manner, and the negative only slightly stim- 

 ulating or retarding positive reacting organs. 



It would also appear as if positive charges had a tendency 

 to produce attenuated or elongated root development. In 

 regard to this point, it would be interesting to ascertain 

 whether positive charges increase geotropic irrittibility. One 

 of the recent conceptions of solutions is that they contain 

 ions which are atoms or groups of atoms positively or nega- 

 tively charged. It has been observed that solutions with a 

 predominant positive charge, such as acids, and those with a 

 predominant negative charge, bases and salts, have a certain 

 definite eff*ect uj)on protoplasm which is identical with those 

 produced by positive and negative electrical stimulation. 

 There is also reason to believe that protoplasm consists of 

 particles which are charged positively and negatively. It is 

 possible that in the proto})lasm of roots and stems (hypoco- 



