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 devel- 
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-ingredients in the plant is va- 
riable within a narrow range; but 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. 
Hil. We have reason to believe that each part or organ, 
(each cell,) of the plant contains a certain, nearly invari- 
able amount of fixed matters, which is indispensable to the 
vegetative functions. Hach-part 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. 
g 3, 
SPECIAL COMPOSITION OF 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- 
