OF PLANTS BY MANURING. 59 



much as all the vegetable matters we turn to ac- 

 count in the formation of humus consist mainly of 

 vegetable fibre. Such, for example, are straw, leaves, 

 saw-dust, moss, turf, and bog-muck. When these 

 substances, as has already happened with turf and 

 bog-muck, turn to putrefaction and decay, their color 

 becomes dark, and they are converted into carbonic 

 acid and water, which can now be absorbed by 

 plants. As a strict nutrient for plants, the sub- 

 stances just named are of subordinate importance, 

 because Nature labors under no deficiency in car- 

 bonic acid and water, and plants can imbibe these 

 elements from the moisture of the soil, without which 

 vegetation is in general impossible, as also from the 

 air, in any quantity they require, provided only that 

 they are supplied with the necessary mineral and 

 azotized materials. Moreover, great anxiety on the 

 farmer's part respecting the introduction of humus 

 into the earth is uncalled for from the fact, men- 

 tioned in page 36, that Nature herself provides 

 against its removal from the soil, when the farmer 

 only takes care that it produces vigorous and abun- 

 dant plants. In Saxony there are several large farms 

 (for example, in Wohla and Lawalde, near Lobau), 

 whose occupants have either altogether, or for the 

 greater part, removed their cattle, and manured 

 their fields, — in no respect rich in humus, — for 

 ten or twelve years past, exclusively with bone- 

 dust and guano ; that is, with substances which 

 supply directly to the land scarcely any humus. 



