106 APPLIED BIOLOGY 



Pour some of the extract into another tube, add a few drops of 

 Fehling's solution (a mixture of copper sulphate and Rochelle salts, 

 used by chemists for testing certain kinds of sugar), heat tube in a 

 flame, and note the red color of the contents. Test some glucose 

 or corn-sirup. Try Fehling's solution on a little starch in water ; 

 does the red color appear? Only sugars like glucose give the red 

 reaction. White granulated sugar from cane and beet does not. 



Change of Starch to Sugar. (D) Boil a small quantity of starch 

 in water in a test-tube, thus making a very thin starch paste. Put 

 half of the paste in a second test-tube and add some diastase (ob- 

 tained by extraction from plant tissues, and sold at drug-stores). 

 After a half-hour, take some liquid from each tube and apply the 

 starch and sugar tests. Results ? Conclusions ? 



To test regarding osmosis : pour the contents of the two test-tubes 

 into two gold-beater's bags and hang the bags in tumblers or beakers 

 containing some water, or use the osmose-apparatus described in 

 398. After allowing an hour or more for osmosis, pour some water 

 from each tumbler into test-tubes, and test with a few drops of 

 Fehling's solution. Also test some of the water for starch, using 

 iodine. Does the starch paste osmose ? Is there sugar in the 

 water having the starch without diastase? Conclusion? 



103. Path of Foods Down the Stem. It has been stated 

 above that the foods (chiefly sugar) derived from the starch 

 of the leaf may go down into the stem or into other parts of 

 the plant connected with the stem. Also, the proteins (com- 

 pounds of C, H, O, with N and other elements) which are 

 mentioned in 101 as being formed in the cells of leaves, may 

 go down into the stem and thence into roots, flowers, fruits, or 

 new branches. Obviously the sugar and proteins in solution 

 cannot go down in the wood-tubes, because in them there 

 is the strong upward current produced by transpiration. 

 Botanists are now agreed that the downward current is in 

 the bark part of the fibro-vascular bundles, and through the 

 tubes previously described ( 70) as sieve-tubes. The move- 

 ment is so slow that it cannot be demonstrated with red 

 ink, as in the case of the wood-tubes ( 92). However, the 

 evidence obtained from other experiments is no less con- 

 vincing. 



