NATURE OF FOOD STORED IN SEEDS 



32. 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 commer- 

 cial 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 of a 

 majority of plants, and 

 abundant in some, as in 

 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. 



33. The presence of grape sugar can be determined by 

 adding a solution of the substance to "Fehling's solution." 

 Grape sugar "reduces" Fehling's solution.* The presence of 

 cane sugar can be determined by adding a solution of cobalt- 

 ous nitrate (5 grains cobalt nitrate in 100 c.c. distilled water) 

 to a solution containing the cane sugar, followed by the addi- 

 tion 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 



* It causes the precipitation of copper and cuprous oxide, a reddish sub- 

 stance. 



St 



Fig. 29. 



Cells from the cotyledon of the pea (Pisum 

 sativum). si. starch grains with nucleus and con- 

 centric striae; a, granules of aleurone; i, i, inter- 

 cellular spaces. After Sachs. 



