386 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 31 



calls for a more complicated solution than the three-salt one. A 

 solution which the writer fonnd to be good for growing tomatoes 

 contained the following ions expressed as parts per million parts of 

 water used : 



Calcium (Ca) 200 



Magnesium (Mg) 60 



Potassium (K) 78 



Nitrate (NO3) 620 



Sulphate (SO*) 290 



Phosphate (PO4) 74 



Manganese (Mn) 1 



Boron (B) 1 



Iron (Fe) Enough to keep plants green. 



The excellent growth made by the plants in this solution can be 

 seen in Plate 2. 



Each ion included in the above list exerts a definite influence on 

 the growth of plants. So characteristic is the effect of the omission 

 of a. single element that the plant itself frequently serves as an 

 index of the element it lacks for normal growth. Again using the 

 tomato plant as an example, a healthy leaf and one taken from a 

 plant suffering from " potash hunger " are contrasted in Plate 3. 

 An insufficient amount of potassium results in a yellowing of the 

 older leaves, which later are covered with brown spots. On the 

 other hand, phosphorous deficiency brings about a deepening of the 

 green color of the leaves, and in severe cases the lower leaf surfaces 

 become distinctly purple and the stem grows out slender and sharply 

 pointed. With extreme calcium deficiency the growing points of the 

 stem soon die and become dry. 



A common method for growing plants in a nutrient solution is, 

 first, to germinate the seeds between layers of moist filter or blotting 

 paper kept in a glass dish and covered to conserve the moisture. 

 When the roots grow to one-fourth to three-fourths of an inch in 

 length these seedlings are transferred to a germination net. Two 

 pieces of paraffined cotton fly netting are stretched and fastened 

 over a suitable dish. It is well to separate the pieces of netting 

 from each other by a piece of bent glass tubing one-fourth of an 

 inch in diameter. Tlie dish is then filled with water and the roots 

 of the seedlings carefully inserted in the meshes of the netting. 

 During the subsequent growth of the seedlings tap water is allowed 

 to flow through the dish. After the seedlings have reached a height 

 of approximately an inch they are transferred to the culture solu- 

 tions. Each culture contains one or more seedlings supported by 

 means of a little cotton in holes of paraffined flat cork stoppers, 

 which fit into the culture jars containing the nutrient solution. The 



