172 GUANO. 



manure-heap; and this can be done only by giv- 

 ing it absorbents, such as peat, sawdust, tan, sods 

 from headlands, loam, or gypsum. Urine is rich in 

 ammonia, and should not be allowed to run to 

 waste. Often the drainings from the manure-heap 

 containing it are permitted to flow away unmo- 

 lested. Unless the soil naturally contains a quan- 

 tity of humus, or has been well manured, fertilizers 

 containing this substance largely — such as night- 

 soil, guano, or urine — cannot be recommended for 

 exclusive application in large quantities. Although 

 experiments have been cited where land has perma- 

 nently retained its fertility under an annual dressing 

 of guano, yet the experience of most farmers has 

 been to the effect, that such treatment produces a 

 certain want of life, and in the end barrenness, 

 while if mixed with the compost-heap it is calcu- 

 lated permanently to increase growth. If it is 

 desirable to stimulate the vigor of the tree, the 

 application of such manures may be well, otherwise 

 they should be withheld. 



Mr. Johnston again says : " The soluble organic 

 substances which enter the circulation of plants 

 through the roots consist not only of carbon and 

 water, but of combinations of hydrogen and oxygen 

 in various proportions. From these substances, 

 therefore, plants derive an uncertain and indefinite 

 supply of hydrogen in a state already half organized, 

 and probably still more easily assimilated or con- 



