CHAP. XII. §. II. IN EOOTS DUBING VEGETATION. 171 



was obtained ; but in the majority of instances the 

 electrode in contact with the soil was positive to the 

 other. The influence of the soil was shewn thus : 

 in those plants which had been recently repotted, 

 and the mould consisted of a mixture of sand and 

 peat earth, the effects were null, and the electrodes 

 when inserted alone in the pots indicated but slight 

 effects ; whereas in those pots in which the earth 

 had remained some time, and consisted of common 

 garden mould, the effects were very decided. Damp- 

 ness of the soil also increased the effect. 



As it was difficult to know when the electrode was 

 in contact with the spongioles, the following method 

 was adopted. 



Broad beans (Windsor) were made to vegetate in 

 the dark in water, and in small glass jars containing 

 but a small quantity of mould. At different periods 

 of vegetation, the apex of the plumula or the stem 

 was removed close to the cotyledons, and a circuit 

 formed between the divided surface and the external 

 surface of the radicle ; the latter was generally 

 positive; in some instances no effect ensued. Sup- 

 posing that the effects might arise from the acidity 

 of the soil, a- dilute solution of potash was poured 

 into the glass jar. Under these circumstances, 

 however, the electrode in contact with the soil was 

 podtive to the other. The whole root was taken out 

 of the soil, and washed gently in water so as to 

 remove the earth, then placed in water, and the 

 circuit reformed; the electrode in contact with the 



