EXPERIMENTAL PLANT PHYSIOLOGY. 



plants may be grown in solutions of different composition. It 

 has been found by numerous experiments and analyses that 

 only potassium, calcium, magnesium, sulphur, phosphorus, iron, 

 and sometimes silica and chlorine are obtained from the soil 

 alone. Of the remaining substances necessary for the plant, 

 hydrogen is obtained from both water and the soil compounds, 

 oxygen from both the soil and the air, nitrogen usually from 

 the soil, but in some instances also from the air, and carbon 

 almost entirely from the air, except in the case of the plants 

 -which derive it from complex compounds. (§§ i, 8, and 9.) 



EXPERIMENT i. 



WATER CULTURES. 



Fill a large bottle with distilled water, and to each liter of water 

 add or 



I. gram potassium nitrate 

 0.5 " sodium chloride 

 0.5 " calcium sulphate 

 0.5 " magnesium sulphate 

 0.5 " calcium phosphate 

 Warm gently for an hour and keep in a dark place. 



Fig. I. 



1. gram calcium nitrate 

 0.25 " potassium chloride 

 0.25 " magnesium sulphate 

 0.25 " acid potassium phos- 

 phate 



Hansen's germinator. A, glass vessel filled with water and covered with 

 tightly-stretched bobbinet. B, bell-jar fitted with moist filler-paper. 

 (Oels.) 



