44 ORIGIN AND ACTION OF HUMUS. 



the family of the Graminetz, or of the Equisetacece, 

 the solid framework of which contains silicate of 

 potash, without silicic acid and potash, or a plant of 

 the genus Oxalis without potash, or saline plants 

 such as the saltworts (Salsola and Salicornia), 

 without chloride of sodium, or at least some salt of 

 similar properties. All seeds of the Grammes con- 

 tain phosphate of magnesia ; the solid parts of the 

 roots of the altlicea contain more phosphate of lime 

 than woody fibre. Are these -substances merely 

 accidentally present ? A plant should not be 

 chosen for experiment, when the matter which it 

 requires for its assimilation is not well known. 



What value, now, can be attached to experiments 

 in which all those matters which a plant requires 

 in the process of assimilation, besides its mere nutri- 

 ment, have been excluded with the greatest care ? 

 Can the laws of life be investigated in an organized 

 being which is diseased or dying ? 



The mere observation of a wood or meadow is 

 infinitely better adapted to decide so simple a ques- 

 tion, than all the trivial experiments under a glass 

 globe ; the only difference is, that instead of one 

 plant there are thousands. When we are acquainted 

 with the nature of a single cubic inch of their soil, 

 and know the composition of the air and rain- 

 water, we are in possession of all the conditions 

 necessary to their life. The source of the different 

 elements entering into the composition of plants 

 cannot possibly escape us, if we know in what form 



