FARMERS' INSTITUTES. 17 



ble and inactive materials, which are of value to the plant by reason of 

 their physical properties, relating to temperature, moisture and me- 

 chanical support of the plant; the mechanical agents of plant growth. 



It is with the second, or reserve class, that the chemist has to do. 

 How to bring the reserve elements of fertility into active use is the 

 great problem of the agricultural chemist. This change is effected 

 incidentally by a great many operations on the farm; plowing, har- 

 rowing, cultivating the soil, draining and tiling, opening up the soil 

 to action of frost, weathering, etc. Anything which will phj^sically 

 modify the condition of the soil will have an incidental influence on 

 the reserve bodies of the soil. Cultivation is not limited to killing 

 weeds; it aids plant nutrition far more by promoting nitrification, for a 

 well cultivated field is a nitre plantation on a large scale. 



What 1 wish to emphasize is the maxim of Dr. Halsted: ''T,he soil 

 is a factory, not a mine." A mine is worked out and abandoned be- 

 cause exhausted. When the present crop of gold is gathered and the 

 last glittering particle is secured, no new crop of gold again appears, 

 even during the lapse of the slow-winged centuries, and the mine is closed 

 forever. Not so the soil. It is a factory — the workshop of God, where 

 his handmaid. Nature, weaves in endless forms the wonderful fabrics 

 of vegetable life — the basis and support of animal life. 



The humus of the soil — remains of former races of plants: — was for 

 a long time regarded as the special means for feeding a new race of 

 plants, and in the long ago of agricultural science King Humus ruled 

 the vegetable world. It was supposed that material that had once 

 gone the rounds of plant life could more readily contribute to the 

 formation of a new generation of plants, securing, as it were, a re-incar- 

 nation of vegetable life. 



But King Humus has lost his crown, and is no longer regarded as 

 the pre-digested food' to sustain a new race of plants. It is only indi- 

 rectly that humus contributes to vegetable growth. His office is hum- 

 bler — to elaborate out of soil the crude materials for another cycle of 

 inanimate life. 



The physical offices of humus in the soil are important, making the 

 soil warmer by one and a half to two and a half degrees for the whole 

 season from May to November, making it more retentive of moisture 

 and holding ammonia from dissipation in the air or washing away 

 in drainage water. Chemically humus is of great importance in the 

 soil, for by its oxidatio?i it is a constant source of carbonic acid. Dis- 

 solved in the soil water it becomes the true carbonic acid, Hg C O3, 

 instead of the less active carbonic oxide. Carbonic acid is among the 

 weakest of acids. It has the touch of velvet, yet it will break barriers 

 of rock. The vast limestone caverns of Virginia, Kentucky and Ten- 

 nessee have been excavated — literally washed out — by water charged 

 bv carbonic acid, so that rivers now flow through these subterranean 

 channels to the sea. Mammoth Cave was dug by carbonic acid. The 

 soil water in our state holds carbonate of lime in solution by means of 

 this acid. 



Not only will this acid dissolve lime, but the ever-acting sapping and 

 mining of this acid breaks up the granite rocks by decomposing the 

 feldspar and mica they contain, and is one of the active agencies by 

 \\hich potash is set free from feldspar and mica. There is a saying 



