ELECTRIC CULTIVATION IN RELATION TO HORTICULTURE. 403 



So soon as these energising rays fall upon the green leaves, the 

 chlorophyll grains commence to act, absorbing the carbon from the 

 carbon-dioxide, and, with the elements of water, producing chemical 

 compounds suitable for assimilation by the plant. 



It will be observed that this sequence of operations relies for its 

 inception upon solar, or voltaic arc actinic rays. It might be argued that 

 this solar ray which switches on the action of the chlorophyll grains is 

 the electrical agency : a flash of electric rays from the arc light or from 

 the sun falls on the green leaf and, presto ! the leaf is energised and 

 the chlorophyll grains begin their work. 



The wet membranes of the leaves allow gaseous exchange ; the 

 carbon-dioxide of the air flows through the moist cellulose membranes 

 into the cells of the leaf along with the moisture, and the considerable 

 surface exposed by leaves permits a large attack of the C0 2 on the 

 exposed and moist membranes. The C0 2 is broken up, the carbon is 

 absorbed by the leaf and the oxygen is liberated, escaping back into the 

 air. The permeability of the exposed leafy membrane is seriously reduced 

 if moisture is not present, hence the great importance, in a dual sense, 

 of moisture. The pores of a leaf when dry become contracted, and offer 

 resistance to the passage of the gaseous C0. 2 and the moisture which 

 carries electrical energy. By the absence of moisture the process of 

 carbon absorption becomes seriously impeded. We may therefore say 

 that both the electrical energy of the sunlight, and the electrical energy 

 stored in moisture, are necessary for the initiation of the function of the 

 leaf so far referred to. 



Independently of the importance of moisture in facilitating gaseous 

 exchange through the leafy membrane, it is important, because the 

 elements of water combine with the carbon to produce within the 

 chlorophyll-bearing cells carbo-hydrates, such as starch. The excess 

 oxygen, as we know, escapes back into the air. 



The energising effect of the electric light or sun's rays continues 

 so long as the sunlight falls upon the leaf ; in fact, it continues a short 

 time after the rays are cut off — a fact of enormous significance, the 

 knowledge of which we owe to the refined investigations of Dr. Waller, 

 F.R.S. 



According to Dr. Waller, the living leaf immediately responds to the 

 stimulus of sunlight, and in a lesser degree to the influence of electric 

 arc light. 



Diffuse daylight only produces slight response. The effect is clearly 

 illustrated by the diagram (fig. 63). The needle of the galvanometer is 

 instantly deflected when the light falls on the leaf, the deflection ranging 

 over — 0*02 volt and + 0-02 volt. When the light rays are cut off the 

 needle slowly falls down to zero, which it reaches after a lapse of thirty 

 minutes from the time the light is removed. 



The rays projected from the sun, with potentials of energy beyond 

 calculation, flow into our planet's atmosphere, becoming gradually diffused 

 in the higher strata. Their density or electrical potential enormously 

 exceeds that of the electric potential of, and near to, the earth's surface, 

 and the energising activity is proportionately greater ; but when the rays 

 pass into hygrometric or water-carrying strata, it is presumed that the 



