SUGARS, OILS AND RESINS 273 



grams in 250 c.c. water; (2) sodium hydroxid, 30 grams in 

 250 c.c. water; (3) Rochelle salts (sodium potassium tartrate), 

 43 grams in 250 c.c. 



456. Cane-sugar is stored as a reserve food in many 

 plants. In the maple tree, sugar-beet, sorghum, and sugar- 

 cane, cane-sugar is abundant. Test the sugar-beet for glu- 

 cose with Fehling's solution. None is found. Boil a piece 

 of sugar-beet in a little water in a test-tube. To the water 

 first add a drop of hydrochloric acid. When cool add a 

 pinch of sodium carbonate and Fehling's solution, and again 

 heat. A precipitate of oxid of copper is obtained. Cane- 

 sugar heated in the presence of hydrochloric acid is con- 

 verted into glucose and fructose. This is one test for cane- 

 sugar. Another test is as follows: (1) Make a thin section 

 of sugar-beet and let it stand a few minutes in a strong 

 solution of copper sulfate. Then carefully rinse off all the 

 salt. (2) Heat in a very strong solution of potassium hy- 

 droxid. There will be seen a blue coloration in the section, 

 gradually washing out into the liquid. 



457. To test for the oil content of the cell: Mount a thin 

 section of the endosperm of castor-bean seed in water and 

 examine with high power. Small drops of oil will be abun- 

 dant. Treat the mount with alcanin (henna root in alcohol). 

 Half an hour or more may be required. The drops of oil 

 will stain red. This is a standard test for fats and oils. 



458. To examine gum-resin: Mount a little of the milky 

 juice of the leaf-stem of the garden poinsettia (Euphorbia 

 pulcherrima). It is of a creamy consistency. Examination 

 under the microscope shows that it is not white, as it seems 

 to the naked eye. The particles are yellowish or colorless 

 and insoluble. These particles are gum-resin. They have 

 been emulsified by the plant, making the juice appear white. 



459. Starch is the most abundant of the solid products 

 of the cell. Starch grains have a definite form for each group 

 of plants; and these groups can be determined by the form 



