WATER CULTURE, PHOTOSYNTHESIS, RESPIRATION. 167 



(7) Pull solution minus Sulphur substitute magnesium 

 nitrate for the magnesium sulphate. 



(8) Full solution minus Phosphorus substitute potassium 

 sulphate for the potassium phosphate. 



(9) As a control to all the other cultures, leave one pair with 

 distilled water only. 



221. Progress of the Cultures. Various steps must be taken 

 in order to ensure success with water cultures. Tie a roll of black 

 paper or cloth round each jar, to darken the roots. Each day add 

 distilled water, to replace that lost by evaporation and absorption 

 take care not to let the cork get wet and stir up the liquid with 

 a rod; also force air into it with a bicycle pump otherwise the roots 

 may suffer from lack of oxygen. 



The solution must not be allowed to become alkaline in reaction ; 

 if it turns red with litmus paper, add a little 5 per cent, phosphoric 

 acid until it is slightly acid in reaction. Once a month pour off the 

 solution in each jar, rinse out the jar with distilled water, fill up 

 the jar with distilled water and let the plants grow in this for a few 

 days before filling the jar again with fresh culture solution. 



Label each jar "Full Solution," "Minus Iron," "Minus Nitro- 

 gen," and so on. Keep a record of the progress of the plants, 

 noting in each case their general characters height, number of 

 leaves, size of leaves, etc. 



In the case of seedlings with large food -containing cotyledons, e.g. 

 Broad Bean, the plant will often show healthy though somewhat 

 meagre growth, and eventually produce flowers and fruits when the 

 roots are supplied only with distilled water. In this plant the 

 cotyledons contain quite sufficient of some at least of the necessary 

 elements, without depending upon external sources. The coty- 

 ledons should therefore be removed from all the plants, when Beans 

 or Peas are used, and this should be done simultaneously when the 

 seedlings are placed in the jars. 



In the absence of iron, the plant produces normal leaves at first, 

 but after a time the new leaves formed are white this condition of 

 chlorosis is readily remedied by either adding an iron salt to the 

 culture fluid or by applying it in very weak solution to the chlorotic 

 leaves, which then turn green owing to the formation of chloro- 

 phyll. Chlorotic culture plants are easily obtained in the Maize or 

 Sunflower ; in the case of Beans, the cotyledons contain enough iron 

 for the whole plant. 



Besides noting that in the absence of the essential elements the 

 plant grows badly, a rough comparison of the amount of increase in 

 each case should be made by drying the seed-raised plants in the 

 incomplete solutions, as soon as they show obvious signs of arrested 

 growth and approaching death, and noting their dry weight as com- 

 pared with that of the seeds from which the plants started. 



