OO SEEDS AND SEEDLINGS. 



compare with the store of food placed at the disposal of 

 young animals e.g. in eggs and in milk ? From their size 

 and thickness, and the fact that they are used as human 

 food, it is easy to infer that the cotyledons of Beans or Peas 

 are storehouses of reserve food- stuffs. 



In addition to carbon the Bean seed contains nitrogenous 

 substances and also some mineral matter (ash ingredients). 

 The Bean seed contains all the chief kinds of human food 

 water, mineral salts, proteids, starch, and oil (scanty). 



* (a) Place a piece of Bean cotyledon on the end of a long needle (a 

 needle mounted in a piece of wood like a penholder is best for purposes 

 like this), and hold it over the flame of a spirit-lamp ; notice that it 

 turns black in a few seconds. Rub the charred mass on white paper ; 

 it leaves a black mark of charcoal (carbon). Continue to heat the piece 

 for some minutes, and note that it burns to ash. 



* (&) Heat some dry Beans or Peas in a test-tube fitted with a bent 

 tube passing through a bored cork, and dip the free end of the tube 

 into lime-water or baryta- water. Notice the white precipitate pro- 

 duced by the carbon dioxide set free. 



* (c) Crush, or cut up into small bits, some Beans or Peas, mix them 

 with three or four times the quantity of soda-lime, and heat the 

 mixture in a test-tube. Fumes of ammonia are given off, proving the 

 presence of nitrogen. 



To make soda-lime, mix two parts of quicklime with one of solid 

 caustic soda and one of charcoal ; moisten with water, mix into a 

 paste, dry thoroughly, and keep the powdered mixture in a corked jar. 



66. Carbohydrates. Starch and sugar both exist 

 abundantly in plants, and are called carbohydrates, because 

 on analysis the proportion by weight of hydrogen to oxygen 

 found united with the carbon is always the same as exists in 

 water viz. 1 : 8. Starch is insoluble in cold water, but is 

 easily converted, by various processes, into sugar, which is 

 soluble. Other carbohydrates are cellulose, gum, inulin, 

 dextrin, glycogen. 



* (a) Heat some dry laundry starch in a test-tube. Note the conden- 

 sation of water in the upper part of the tube. This proves the 

 presence of hydrogen and oxygen in starch (since water is composed of 

 these elements). Note also that the starch soon begins to blacken, 

 proving that it contains carbon, and at the same time dirty white 

 fumes are evolved, having a pungent odour somewhat resembling 

 that of burnt sugar. Apply a light to the mouth of the test-tube 

 the fumes are inflammable ; introduce a piece of moist blue litmus 

 paper into it the litmus becomes red, showing that the fumes are 



