166 WATER CULTURE, PHOTOSYNTHESIS, RESPIRATION. 



To make a O'l per cent, solution, which is quite strong 

 enough for water culture experiments, add 5 litres of 

 water to 1 litre of the stock solution ; then add a few 

 drops of 5 per cent, solution of an iron salt, e.g. chloride, 

 so that the complete solution contains a trace of iron. 



220. Water Culture Experiments. In order to get 

 good average results, we require to set up nine sets of 

 cultures with two or three similar plants in each set in 

 case of anything going wrong as well as to eliminate 

 individual differences. The nine sets are wanted for 

 growth in (1) full culture solution; (2) solution minus 

 Iron ; (3) solution minus Calcium ; (4) solution minus 

 Magnesium ; (5) solution minus Potassium ; (6) solution 

 minus Nitrogen ; (7) solution minus Sulphur ; (8) solution 

 minus Phosphorus ; (9) distilled water. 



One kind of plant must, of course, be u;ed throughout the ex- 

 periments. Good results may be obtained with seedlings of Bean, 

 Pea, Wallflower, Maize, Oats ; or cuttings of Willow, Fuchsia, 

 Horse Chestnut, Tradescantia, etc. Try different plants each time 

 you start a series of cultures. If seedlings are to be used, select 

 seeds as nearly alike in weight as possible, weigh a batch of seeds, 

 determine the average dry weight ; then soak the seeds and sow 

 them in a germination jar or in moist sphagnum or sawdust. When 

 the roots are several centimetres long, select seedlings as nearly alike 

 in development as possible ; fill the jars with distilled water to 

 within about 5 cm. of the top so that the cover and the seed itself 

 shall not be wetted and fit a seedling into each jar so that its root 

 dips into the water. 



For four or five days allow the plants to grow in water. Then 

 take the jars in pairs and treat each pair as follows : 



(1) Pull solution replace the water with the complete culture 

 solution. 



(2) Full solution minus Iron omit the iron compound. 



(3) Pull solution minus Calcium substitute (in equal amount) 

 potassium nitrate for the calcium nitrate. 



(4) Full solution minus Magnesium substitute potassium 

 sulphate for the magnesium sulphate. 



(5) Pull solution minus Potassium substitute calcium phos- 

 phate for the potassium phosphate. 



(6) Full solution minus Nitrogen substitute calcium phos- 

 phate for the calcium nitrate. 



