160 HOW CROPS GROW. 



It is, of course, impossible to attempt producing a plant 

 at all without some ash-ingredients, for the latter are 

 present in all seeds, and during germination are trans- 

 ferred to the seedling. By causing seeds to sprout in a 

 totally insoluble medium, we can observe what happens 

 when the limited supply of fixed matters in the seeds them- 

 selves is exhausted. Wiegmann & Polstorf (Preisschrift 

 uber die unoryanisclien Bestandtheile der Pflanzen] plant- 

 ed 30 seeds of cress in fine platinum wire contained in a 

 platinum vessel. The contents of the vessel were moist- 

 ened with distilled water, and the whole was placed under 

 a glass shade, which served to shield from dust. Through 

 an aperture in the shade, connection was made with a gas- 

 ometer, by which the atmosphere in the interior could be 

 renewed with an artificial mixture, 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 ap- 

 pearance during 26 days, reaching a height of two or 

 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 weighed pre- 

 cisely as much as that obtained by burning 28 seeds like 

 those originally sown. This experiment demonstrates 

 most conclusively that a plant cannot grow in the absence 

 of those substances found in its ash. The development 

 of the cresses ceased so soon as the fixed matters of the 

 seed had served their utmost in assisting the organization 

 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 unhealthiness, 

 they would have recovered, and developed to a much great- 

 er extent. 



II. The proportion of ash-ingredients in the plant is 

 variable within a narrow range, but cannot fall below or 

 exceed certain limits. The evidence of this proposition 



