146 HOW CROPS GROW. 
We may conclude this section by stating three proposi- 
tions which are proved in part by the facts that have been 
already presented, and which are a summing up of the 
most important points in our knowledge of this subject. 
I. Ash-ingredients are indispensable to the life and 
growth of all plants. In mold, yeast, and other plants of 
the simplest kind, as well as in those of the higher orders, 
analysis never fails to recognize a proportion of fixed mat- 
ters. We must hence conclude that these are necessary to 
the primary acts of vegetation, that atmospheric food can- 
not be assimilated, that vegetable matter cannot be organ- 
ized, except with the codperation of those substances, which 
are found in the ashes of the plant. This proposition is 
demonstrated further in the most conclusive manner by 
numerous synthetic experiments. It is, of course, impos- 
sible to attempt producing a plant at all without some ash- 
ingredients, for the latter are present in all seeds, and dur- 
ing germination are transferred to the seedling. By caus- 
ing seeds to sprout in a totally insoluble medium, we can 
observe what happens when the limited supply of fixed 
matters in the seeds themselves is exhausted. Wiegmann 
& Polstorf, (Preisschrift tiber die unorganischen Bestand- 
theile der Pflanzen,) planted 30 seeds of cress in fine plati- 
num wire contained in a platinum vessel. The contents 
of the vessel were moistened with distilled water, and the 
whole was placed under a glass shade, which served to 
shield from dust. Through an aperture in the shade, con- 
nection was made with a gasometer, by which the atmos- 
phere in the interior could be renewed with an artificial mix: 
ture, consisting in 100, of 21 parts oxygen,78 parts nitrogen, 
and 1 part carbonic acid. In two days 28 of the seeds 
germinated; afterwards they developed leaves, and grew 
slowly with a healthy appearance during 26 days, reaching 
a height of two to three inches. From this time on, they 
refused to grow, began to turn yellow, and died down. 
The plants were collected, and burned; the ash from them 
f 
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