SEEDS AND SEEDLINGS 71 



previously prepared. Heat the mixture, which should now have 

 a blue color, in the test tube. If grape sugar is present in consid- 

 erable quantity, the contents of the tube will turn first a greenish, 

 then yellow, and finally a brick-red color. Smaller amounts will 

 show less decided red. No other substance than sugar will give 

 this reaction. If Benedict's test 1 is used, a colored precipitate 

 will appear in the test tube after boiling. 



Starch changed to Grape Sugar in the Corn. That starch is 

 being changed to grape sugar in the germinating corn grain can 

 easily be shown if we cut lengthwise through the embryos of half 

 a dozen grains of corn that have just begun to germinate, place 

 them in a test tube with some Fehling's solution, and heat almost 

 to the boiling point. They will be found to give a reaction show- 

 ing the presence of sugar along the edge of the cotyledon and 

 between it and the endosperm. 



Digestion. This change of starch to grape sugar in the corn 

 is a process of digestion. If you chew a bit of unsweetened cracker 



1 BENEDICT'S TEST FOR GRAPE SUQAB 



This test, known from its author as "Benedict's test," will be found described 

 iu the 1909 edition of Hawk's Biochemical Chemistry. In the latter it is the one 

 labeled "Second Solution." 



PREPARATION 



Copper sulphate 17.3 grams 



Sodium citrate 173. grama 



Sodium carbonate (anhydrous) . . . 100. grams 

 Make up to 1 liter with distilled water 



With the aid of heat dissolve the sodium citrate and carbonate in about 600 c.c. 

 of water. Pour through folded filter paper into a glass graduate and make up to 

 850 c.c. with distilled water. 



Dissolve the copper sulphate in about 100 c.c. of water and make up to 150 c.c. 

 with distilled water. 



Pour the carbonate-citrate solution into a large beaker or casserole and add 

 the copper sulphate solution slowly with constant stirring. 



The mixed solution is ready for use and does not deteriorate on standing. 



For use add to 5 c.c. of the solution in a test tube 8 drops (more does not disturb 

 the experiment, but 8 drops is sufficient for a good result) of the solution under 

 examination. Boil for one or two minutes and let cool. If grape sugar be present, 

 the entire body of the liquid will be filled with a precipitate which may be red, 

 yellow, or green in color, depending upon the amount of sugar present. Eight 

 drops of 1 per cent dextrose will yield precipitates of large amounts. 



The positive reaction is the precipitate, not the color. On this account the test 

 may be applied as well in artificial light as in daylight. 



