174 PLANT LIFE. 



into contact with them. On the contrary, the oxygen seems 

 to enter into loose comljinalion with jjrotoplasm, forming 

 an exti-emely unstable compound which under unknown con- 

 ditions breaks down into simpler stibstances, setting free 

 energy. Some of these materials are again used in building 

 protoplasm, while others break down still further, ultimately 

 into water and carbon dioxide. The supply of oxygen is so 

 necessary that if a plant cannot obtain oxygen from without, 

 it will secure it by the destruction of jiart of its own sub- 

 stance for a time, as shown by intramolecular respiration. 



248. Heat. — While this decomposition of the protoplasm 

 in ordinary respiration is not a true oxidation, it nevertheless 

 results, as oxidation does, in the evolution of heat. The 

 amoimt of heat produced is usually not great enough, and its 

 loss too rapid, to make it readily perceptible. Anything 

 which prevents the radiation of heat will make its measure- 

 ment possible. The germination of large quantities of seeds 

 or the blossoming of a number of tlowers in a confined space 

 may raise the temperature as much as 15 or 20° abo\'e that 

 of the ail'. The heating of hay, grain, and sinn'lar substances, 

 which have been stored when moist, is due partly to the 

 respirator)' activity of bacteria and fungi, which grow ra[)idly 

 under these conditions. l*'ennentati\e changes, which also 

 occur under the same conditions, add to the c\olution of 

 heat. 



249. Light. — A few ])lants also produce light. This light 

 is like that seen when ]ihosp]iorus is exposed to the air in 

 darkness, or M'hen the end of a match is lightlv rubbed. 

 Phosphorescence occurs only in some bacteria and fungi. 

 When it is seen upon de(-a)-ing meat, fish, or wood, it is 

 because these organisms are present. It does not arise from 

 the decaying substance itself Se\'eral of the larger fungi, as 

 certain toadstools, have a mycelium cajiable of emitting this 

 phosi)hores( ent light. 



