SEEDS AND SEEDLINGS. 33 



a good deal of carbon dioxide is given off under such 

 conditions, as is shown by the following experiments. 



* (a) Soak some Peas in water for a day, so that their coats can be 

 removed without damaging the embryo (the coats are removed so as to 

 avoid introducing air with the seeds). Fill a test-tube with mercury 

 and invert it in a dish of mercury ; then pass six peeled Peas under 

 the open end of the tube, when they will float up to the closed end. 

 In a day or so the test-tube is half full of gas : what is this gas, and 

 how has it been produced ? With a bent tube pass a little water under 

 the test-tube, so that it will float up to the surface of the mercury, 

 then pass up a small piece of potash ; the potash solution thus formed 

 absorbs the gas, and the mercury rises again to its original position. 



This production of carbon dioxide, in the absence of free oxygen, is 

 called " intra-molecular respiration"; apparently in some way the 

 substance of the embryo is decomposed in this process, and besides 

 carbon dioxide, alcohol and other products are formed. This process 

 is very marked in Peas and Beans. In all cases it is a process of 

 destruction, without healthy growth taking place. 



* (6) Another method, good for demonstration to a class, is to use the 

 "Torricellian vacuum." Pass a few peeled Peas into the vacuum at 

 the top of a 33-inch tube filled with, and inverted over, mercury. The 

 "vacuum" at the top of the tube contains mercury vapour, but 

 no air. Test, after a day or two, with caustic potash as in the pre- 

 ceding experiment. Note" the height of the column (1) after the Peas 

 are passed up, (2) after the column is depressed by the carbon dioxide 

 formed, and (3) after the absorption of this gas by the caustic potash. 

 In each case note also the reading of the barometer at the time 

 (why ?). 



In each case, as a control experiment, use Peas which have been 

 killed by boiling in water : is carbon dioxide produced by killed 

 seeds ? 



58. Heat produced by Respiration. From the fore- 

 going experiments it is clear that respiration is a process of 

 oxidation, just as burning is, and this suggests that it may 

 be accompanied by the giving out of heat. Do germinating 

 seeds give out heat ? 



(a) Fit three tumblers or jars with a cork or a cardboard cover, with 

 a hole in the centre through which a thermometer is passed. First 

 compare the readings of the three thermometers by placing them 

 together in water at different temperatures. Half-fill one jar with 

 soaked seeds (Peas, Beans, Wheat, or Barley answer well) ; the second 

 with seeds that have been killed by boiling (add some corrosive 

 sublimate to the water to prevent growth of Moulds or Bacteria) ; 

 the third with moist sawdust (as a control). Place the three jars, 

 with thermometers inserted to equal depth in each, in a box, and 

 put dry sawdust between and around them ; cover the whole with 



S.B. 3 



