THE ASH OF PLANTS. 147 



weighed precisely as much as that obtained by burning 28 

 seeds like those originally sown. This experiment demon- 

 strates most conclusively that a plant cannot grow in the 

 absence of those substances found in its ash. The derel- 

 opment of the cresses ceased so soon as the fixed matters 

 of the seed had served their utmost in assisting the organ- 

 ization of new cells. We know from other experiments 

 that, had the ashes of cress been applied to the plants in 

 the above experiment, just as they exhibited signs of un- 

 healthiness, they' would have recovered, and developed to 

 a much greater extent, 



II, The proportion of ash-ingreMents in the plant is va- 

 riable within a narrow range ; hut cannot fall below or 

 exceed certain limits. The evidence of this proposition is to 

 be gathered both from the table of ash-percentages, and 

 from experiments like that of Wiegmann & Polstorf above 

 described. 



nil We have reason to believe that each part or organ, 

 {each cell,) of the plant contains a certain, nearly invari- 

 able amount affixed matters, which is indispensable to the 

 vegetative functions. Ea/^hpart or organ may contain, be- 

 sides, a variable and unessential or accidental quantity of 

 the same. What portion of the ash of any plant is essen- 

 tial and what accidental is a question not yet brought 

 to a satisfactory decision. By assuming the truth of this 

 proposition, we account for those variations in the amount 

 of ash which cannot be attributed to the causes already 

 noticed. The evidences of this statement must be reserv- 

 ed for the subsequent section. 



§ 3. 



SPECIAL COMPOSITION DF THE ASH OF AGRICULTURAL 



PLANTS. 



The results of the extended inquiries which have been 

 recently made into the subject of this section may be con- 



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