98 OP FERTILIZERS. 



garden. Prof. Nuttall, who brought to this country many 

 beautiful wild plants from Oregon, often said that when 

 he saw them in the gardens of those to whom he had sent 

 them, he could hardly recognize them, so much had they 

 been improved in size and vigor by cultivation. 



827. But humus is slowly prepared by the wild plants 

 themselves. The lichen which encrusts the surface of a 

 rock has no humus to begin to live on. It seems to have 

 the power of eating into the rock itself and of extracting 

 thence the mineral elements it needs. From the air and 

 the rain it gets carbonic acid and ammonia, and, when it 

 dies, deposits on the rock a thin coat of humus fitted for 

 the partial nourishment of other generations of lichens. 

 These are succeeded, after many years, by plants some 

 what more fleshy, like the mosses ; and by the grasses and 

 other slender, longer rooted plants ; and these by plants 

 still larger ; till, in the slow process of time, substance 

 enough is gathered to give foothold to shrubs, and finally 

 to trees. 



328. The trees of the forest, by their annual deposit of 

 leaves and, from time to time, of fruits, and at last by the 

 fall and decay of their trunks, prepare a deep bed of 

 humus or forest mould for the use of the husbandman. 



Whenever he can, he avails himself of this treasure. 

 But where it is wanting or scanty, cultivated plants are 

 to be furnished with the abundant humus which they 

 need, by placing in the soil, within reach of their roots, 

 organic, that is to say, vegetable and animal substances, 

 in the state of decay. 



329. How these act has already been shown. They pos 

 sess themselves and impart to the soil the power of absorb- 

 in.tr and retaining, for the use of plants, the water and 

 witli it the carbonic acid, ammonia, oxygen, nitric acid 



