STUDY OF FOODS 



XIX.— Necessity of Food. 



Apparatus. — Wide-mouthed bottles, corks to fit, pea or corn seed- 

 lings, nutrient solution,^ test tubes, paraffin wax, distilled water. 



Directions. A. Take one of the pea or corn seedlings and 

 cut off the cotyledons close to the stem. 

 Pass this through a hole in one of the 

 corks, and insert in a bottle as shown 

 in Fig. 11. Fill the bottle about three 

 quarters full of the nutrient solution. 

 Prepare a second seedling in the same 

 way (select one of as near the same size 

 as possible), but substitute distilled 

 water for the nutrient solution. Note 

 the growth of each seedhng for several 

 days. Do they grow equally fast? 

 What sort of food is in the nutrient solu- 

 tion? From the composition of the 

 water and the mineral salts, is it possible for the plant to 

 get its carbon from the nutrient solution? (Air contains a 

 small proportion of carbonic acid gas [see Ex. V] and plants 



Fig. 11. 



iNutrient Solution after Sachs ('82). 



Distilled water (HgO) 1000.00 



c.c. 

 gram 



Potassivim nitrate (KNO3) 1 • 00 



Sodium chloride (NaCl) 0.50 



Calcium sulphate (CaSOi) 0. 50 



Magnesium sulphate (MgSOi) 0.50 



Calcium phosphate (Cas [P04J2) 0. 50 



Ferric chloride (FeCy 0.005 



(Do not put the ferric chloride into the solution in the first place, but add 

 a drop of it to each bottle when the seedUngs are put in.) 



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