HOfV PLANTS OBTAIJV THEIR LIQUID FOOD. 35 



good. The seeds of these plants may be germinated, after soaking them for 

 several hours in warm water, by placing them between the folds of wet paper 

 on shallow trays, or in the folds of wet cloth (see demonstration I). At the 

 same time that the seeds are placed in damp paper or cloth for germination, 

 one lot of the soaked seeds should be planted in good soil and kept under the 

 same temperature conditions, for control. When the plants have germinated 

 one series should be grown in distilled water, which possesses no plant food ; 

 another in the nutrient solution, and still another in the nutrient solution to 

 which has been added a few drops of a solution of iron chloride or ferrous 

 sulphate. There would then be four series of cultures which should be 

 carried out with the same kind of seed in each series so that the comparisons 

 can be made on the same species under the different conditions. The series 

 should be numbered and recorded as follows : 



No. I, soil. 



No. 2, distilled water. 



No. 3, nutrient solution. 



No. 4, nutrient solution with a few drops of iron solution added. 



70. How to set up tj_e experiment. — Small jars or wide-mouth bottles, or 

 crockery jars, can be used for the water cultures, and the cultures are set up 

 as follows : A cork which will just fit in the 

 mouth of the bottle, or which can be supported 

 by pins, is perforated so that there is room to 

 insert the seedling, with the root projecting 

 below into the liquid. The seed can be 

 fastened in position by inserting a pin through 

 one side, if it is a large one, or in the case 

 of small seeds a cloth of a coarse mesh can 

 be tied over the mouth of the bottle instead of 

 using the cork. After properly setting up the 

 experiments the cultures should be arranged in 

 a suitable place, and observed from time to 

 time during several weeks. In -order to obtain 

 more satisfactory results several duplicate series 

 should be set up to guard against the error 

 which might arise from variation in individual 

 plants and from accident. Where there are 

 several students in a class, a single series set 

 up by several will act as checks upon one an- 

 other. If glass jars are used for the liquid cultures they should be wrapped 

 with black paper or cloth to exclude the light from the liquid, otherwise 

 numerous minute algse are apt to grow and interfere with the experiment. If 

 crockery jars are used they will not need covering. 



Fig. 19. 



Culture cylinder to show position 

 of corn seedling (Hansen). 



