20 BOARD OF AGRICULTURE. 



produced on any land is measured by the minimum quantity 

 of the elements of nutrition contained within the soil. That 

 is, that if in the soil there is a very small per cent., for 

 instance, of lime, the quantity of crop which that laud can 

 produce will be measured by that minimum quantity, or 

 the quantity of lime in the soil ; and so with all the other 

 elements of nutrition. 



The next point of agreement in belief is in relation to the 

 condition in which all the elements of nutrition must exist in 

 the soil, and the manner in which the plant obtains that nutri- 

 tion. It is the universal belief of scientific men who have 

 examined this subject, that mere quantity is of no account ; that 

 coarse, crude, enormous bulk is of no account ; but that the 

 right proportion of the elements in a solvent condition is the 

 standard of the amount of crop production in any given soil ; 

 not bulk, not mass, not enormous quantity, but certain ele- 

 ments of plant-nutrition in a solvent form, and in no other 

 form. These alone can nourish plants. 



Then they are agreed in relation to the manner in which 

 plants obtain their food. And first in relation to the manner 

 in which plants obtain their organic food, — the four elements, 

 carbon, oxygen, hydrogen and nitrogen, — all absolutely essen- 

 tial to the plant. Take carbon first, if you please. Carbon in 

 the plant is never obtained in the form of carbon, but in the 

 form of a compound of carbon and oxygen — carbonic acid. 

 In this form and this alone : carbonic acid taken from the air, 

 or washed from soil-water in precipitation, — carbonic acid in 

 the soil either formed by the action of oxygen on the carbon- 

 aceous material of the soil, absorbed by the water, and 

 thrown by the vital force to the leaves, or carbonic acid taken 

 from the air by absorption in the leaves, there to be decom- 

 posed, the carbon retained, united with the elements of water, 

 passing now down the plant and going through the chemical 

 chauges in its passage to the tissues and to the inner bark of 

 the plant, thrown out in difierent parts of the plant, from the 

 inner tissues of the bark, forming the vegetable oils, the 

 acids, the gum, the starch, the sugar, and the woody fibre of 

 the plant-cellulose — the cellular tissue. This is the way in 

 which the plant obtains its carbon ; in this way, and by these 

 organs of the plant. The nitrogen and the hydrogen of the 



