i8 



GROWTH AND WORK OF PLANTS 



grains with those in ungerminated seeds, the results of the cor- 

 rosion are clearly seen. 



25. Sugar. Sugar is a substance closely related to starch. 

 Commercial sugar is usually in the form of crystals, or when 

 liquid it is known as syrup or molasses. In the plant it occurs 

 in the liquid form since it is dissolved in a quantity of water. 



If it were thick like molasses, 

 or in the form of crystals like 

 commercial sugar, it would 

 be so strong as to kill the 

 plants because it would draw 

 so much water, by absorp- 

 tion, from the surrounding 

 tissue, that the protoplasm 

 would be destroyed. The 

 sugars found in plants are of 

 three general kinds: cane 

 sugar or sucrose abundant in 

 sugar cane, sugar beet, sugar 

 maple, etc.; fruit sugar or 

 glucose found in the fruit 



Fig- 26. . 



Cells from the cotyledon of the pea (Pisum sati- OI a majority Ot plants, and 

 vum). st. starch grains with nucleus and concentric i j 



stride; a, granules of aleurone; *, i, intercellular abundant in Some, aS in 

 spaces. Alter Sachs. i 



apples, pears, grapes, etc., 



(in many fruits and other parts of plants both glucose and cane 

 sugar are present) ; and malt sugar or maltose, as in malted barley. 



26. The presence of grape sugar can be determined by add- 

 ing a solution of the substance to " Fehling's solution." Grape 

 sugar " reduces " Fehling's solution. It causes the precipitation 

 of copper and cuprous oxide, a reddish substance. The presence 

 of cane sugar can be determined by adding a solution of cobaltous 

 nitrate (5 grains cobalt nitrate in 100 cc. distilled water) to a solu- 

 tion containing the cane sugar, followed by the addition of a strong 

 sodium hydrate solution. A beautiful violet color appears. Grape 

 sugar treated in the same way gives a blue color which gradually 

 changes to green. Cane sugar can be changed to grape sugar (or 



