'84 PHYSIOLOGY OF NUTRITION. 



31. Phosphorus, Sulphur, Potassium, Calcium, Magnesium, and 

 Iron, are Necessary for the Higher Plants. 



We cultivate plants, e.g. maize plants, by the water-culture 

 method, as described in 1, but using a complete food solution of 

 somewhat different composition. It contains per litre,- in addition 

 to a very small quantity of Ferric chloride, 1 gr. of Calcium 

 nitrate, O5 gr. of Potassium chloride, O5 gr. of Magnesium 

 sulphate, and 0'5 gr. of finely powdered Calcium phosphate 

 (Ca 3 (P0 4 ) 2 ). This last is very sparingly soluble in water, and 

 therefore forms a sediment in the culture vessel. We further 

 prepare a solution devoid of potash, the Potassium chloride of the 

 complete food solution being replaced by O5 gr. of Sodium chlo- 

 ride. We make a third solution free from Phosphoric acid, the 

 Calcium phosphate being replaced by O5 gr. of Calcium sulphate. 

 A solution free from iron is obtained by leaving out the Ferric 

 chloride. The culture vessels, after they have been fitted up with 

 maize plants, are all exposed to the same external conditions. 

 It is found that the plant in the complete food solution thrives 

 extremely well, while those in the solutions wanting in potash 

 and Phosphoric acid respectively soon cease to grow, when, viz., 

 the small quantities of these substances stored in the seed are 

 exhausted. Potassium and Phosphorus are therefore absolutely 

 essential. The culture in the solution free from potash teaches 

 still further that Potassium cannot in higher plants be replaced 

 in nutrition by Sodium, which chemically is so nearly related to 

 it. Solutions devoid of sulphur are also easily prepared. 



Plants grown in solutions devoid of iron produce at first normal 

 green leaves. Yery soon, however, they begin to appear sickly ; 

 in fact, when the iron in the seed has been used up, they become 

 icteric and chlorotic. The new leaves are no longer green, but 

 white, and microscopic examination of them shows that abnormal 

 chlorophyll bodies, or none at all, are present in their cells. If 

 we add to the food solution a few drops of dilute Ferric chloride 

 solution, the previously white leaves become green in two or 

 three days, and the growth of the plants now proceeds normally. 1 



We may also conveniently work with the following food 

 solutions. We shall find that in the normal solution our plants 

 flourish well, but that with solutions wanting in one substance or 

 another they soon die. 



All the solutions except the last one, containing no Phosphoric 



