146 HOW CEOPS 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 cooperation 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 uber die iinorganischen 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 asli from them 



