350 Comparative Physiology. 



rents of electricity react on and increase vital force. Experi- 

 ments made on the atmosphere near hedges and woods show that 

 it is there in a more negative, or minus, state, from the attrac- 

 tions exerted by the vegetating points ; and plants act on the 

 positive state of vapour in the air, and produce thus condens- 

 ation and rain. Thomas Pine, Esq., {Polytech. Journal) found 

 the point of a living plant to draw off electricity from the 

 prime conductor of a machine at the distance of 14 ft., col- 

 lecting also dew at the point, while the magnetic needle acted 

 only at 4 ft. distance. He found vegetation more powerful 

 when the atmosphere only was electrified, than when electricity 

 was communicated to the soil only. The atmospherical apparatus 

 of Mr. Cross, placed among trees, was found to collect much less 

 electricity, owing to the attraction of plants, than when among 

 houses. Mr. Pollock found that water produced a chemical action 

 affecting the galvanometer, when it Avas added to a coloured 

 solution, but produced no action upon a transparent solution, 

 seeming merely diluted ; a white colour producing reflection, 

 and no absorption or conduction, while dark-coloured absorb- 

 ing substances absorb light and conduct electricity : in every 

 change of colour, he says, in a solution by heat, there is an 

 action on the galvanometer. The film of iodine on the da- 

 guerreotype plate, Avhich at first repels the vapour of mercury, 

 is changed in its electric condition by the action of light, 

 and attracts the vapour ; light has thus the power of exciting 

 an electric condition, if not itself combined with electricity. 

 Electrical light is said to pi-oduce the same effect on the da- 

 guerreotype plate as sun light. Heat, light, and electricity repel 

 and elicit each other ; the passage of electricity always produces 

 a change of atoms in the conductor, and frequently produces 

 both heat and light. Heat developes electricity, as seen in 

 high-pressure steam ; and heat and light mutually render each 

 other sensible, accompanying each other in all bodies, and the 

 developement of the one being generally followed by the other. 

 It becomes, therefore, a very complicated task to which of 

 these agents to ascribe the phenomena that take place. It has 

 been said that negative electricity, which gives its spark in the 

 form of a pointed star, is concerned in forming the fibrous 

 elongated thread-like vessels, whilst the positive, which gives 

 out its spark in the form of a brush, is concerned in forming 

 cellular vessels; it is probably, however, only conjectural. 



The vitality of seeds has been said by some to depend on elec- 

 tricity, but electricity will not rouse the dormant vital power; 

 the capability of exhibiting vital action seems to depend more 

 on their retaining solidity and moisture ; as vital action is set to 

 work, it will likely, however, by the chemical action produced, 

 develope electricity. The reason wliy seeds vegetate soonest at 

 the negative pole is said to be from the alkaline substances 



