CALX INCREASING THE SUPPLY OP CARBON. 249 



other. We must correctly infer that the deeper the green colour, 

 from whatever cause it may proceed in part (as rich manuring, 

 bright sunlight, or moist season), the greater must be the absorp- 

 tion of carbon by the leaves of the plant. Therefore, if in any 

 manner tfye intensity of the green colour of plants is increased, it 

 is equivalent to giving them the power of absorbing and assimilat- 

 ing more carbon, and with that (as before stated), the power of 

 taking up and assimilating the required proportional quantities of 

 oxygen and hydrogen. 



- Now one of the earliest and most manifest effects produced by 

 adding calcareous earth to a soil before extremely needing that ma- 

 nure, is to give a deeper green colour to the plants. This effect is 

 so remarkable on young corn, growing on soil previously acid and 

 recently marled, that before the plants are four inches high, the 

 outlines of the spot made calcareous may be distinctly seen and 

 easily traced by any observer, merely by the strong contrast be- 

 tween the deep green colour of the plants on one side, and the 

 palef yellowish, and sickly green of the other ; and this before there 

 is any obvious difference of size of the plants. And this difference 

 of colour remains so strongly impressed, that a strip of corn thus 

 treated, when of more advanced growth, may be distinguished at 

 the distance of half a mile, if exposed to view so far. 



This early and marked effect of calcareous manures, of giving * 

 deep green colour to plants, I had formerly ascribed solely to the 

 neutralizing of the noxious acid of the soil. And this is doubtless 

 the cause in part. But more extended observations, and the abid- 

 ing effects of this kind, induced me to believe that a direct, as 

 well as the supposed indirect action was produced. But from 

 whatever cause it proceeds, it is unquestionable that the increase 

 of green colour is accompanied by proportionate increase of sup- 

 plies of atmospheric food to the plants, and proportionate increased^ 

 products of the crops for the food of animals, and for food (or 

 manure) for the soil. 



One other well-known agricultural fact will be cited in support 

 of this position. When gypsum (sulphate of lime) is applied to 

 clover, on a neutral soil (where there is no injurious excess of acid 

 to affect the crop, or to be removed by lime), and the gypsum acts 

 well, one of the earliest and most striking evidences of its benefi- 

 cial action is seen in the deeper green colour of the clover dressed, 

 compared to any omitted portions. This effort, however produced 

 (as said before), is equivalent and proportioned to an increased ab- 

 sorption of carbon from the atmosphere j and, as in the previous 

 case, must be ascribed to the increased power of absorption given 

 to the clover by the lime which is the base of the gypsum. 



It may perhaps be questioned that such great effect can be pro- 

 duced by the operation of so small a quantity of lime as is con- 



