12 WHAT THE PLANT IS MADE OF [chap. 



with burning and breathing may be further demonstrated 

 by showing that heat is given off during the process. 

 To prove this, a pair of sensitive thermometers are 

 necessary, reading to a tenth of a degree ; put a mark 

 on each and let them stand in the same jar of water for 

 a time to note any difference in their readings. Mean- 

 time, soak about a pint of peas, or mustard, or barley in 

 water for a few hours, drain off the water, put the peas 

 in a jar and plunge the thermometer into their midst. 

 Fill up another jar with water, in which insert the 

 second thermometer, wrap both jars in flannel to reduce 

 losses of heat, and then stand the pair in some place 

 where they are screened from any but slow changes of 

 temperature, as in an inner cupboard of a room with- 

 out a fire. In a day or two, when germination has 

 set in actively, the thermometer among the seeds will be 

 standing permanently higher than the other one which 

 indicates the normal surrounding temperature. With 

 this further proof we may conclude that germination is 

 a process of breathing or burning, in which some of the 

 seed material combines with the oxygen of the air to 

 produce carbon dioxide and water ; only by this sort of 

 burning does the infant plant get the energy to go on 

 living and working. Indeed, even while the seed is dry 

 and apparently dormant it is breathing very slowly, and 

 so consuming part of its substance; being dry, the 

 embryo cannot draw upon the materials in the endosperm, 

 but is confined to burning up any spare material it 

 possesses within itself. Hence seeds cannot live for 

 ever ; they vary very greatly in their powers of endurance, 

 both with the kind of seed and the way they are stored, 

 but very few of the ordinary farm and garden seeds 

 remain alive after ten years. The embryo is found to 

 perish and shrivel up, though the endosperm or coty- 

 ledons remain perfectly sound ; the slow combustion 



