were exposed to the electric light. To render this 

 visible, immerse the leaf in a weak solution of 

 iodin, and the letter or figure will stand out in a 

 blue color. 



In considering the action of atmospheric elec- 

 tricity upon vegetation, we have to deal with a 

 stimulus which exists in abundance. Plants grow 

 most vigorously where it is most abundant, and 

 with greatest rapidity in the early morning when 

 the dew is more plentifully upon them, making 

 them better conductors. Its most important action 

 upon the stalks of plants is that of increasing their 

 circulation of sap. 



Discharges of electricity in the air, especially 

 during thunder-storms, cause some union between 

 the oxygen and nitrogen in the vicinity of the dis- 

 charges, forming oxides of nitrogen, which, being 

 soluble in water, are carried to the roots of plants 

 and absorbed by them directly. 



Electricity passed through the soil by earth-bat- 

 teries, the geomagnetifer, or other means, has some 

 action upon its chemical constituents. We are 

 familiar with the effects of a current of electricity 

 upon water (OH 2 ) when the electrodes of a battery 

 are placed in it: from each molecule of water two 

 atoms of hydrogen go to the negative electrode 

 and one atom of oxygen to the positive. Since the 

 time when Davy decomposed the alkalies, soda and 

 potash, by means of electricity, nearly every com- 

 pound has yielded to this mysterious power, which, 

 as it were, shakes their molecules until the atoms 

 composing them fly apart. In like manner cur- 



