PHYSIOLOGY 481 



consumed by the plant in respiration, and are the principal source 

 of energy upon which it draws in the metabolic processes. While 

 respiration is not, as a rule, active enough in most plants to raise the 

 temperature to a degree comparable to that found in warm-blooded 

 animals, still, where respiration is active it may be very percep- 

 tible. A thermometer thrust into a mass of actively germinating 

 seeds will show a rise of several degrees, while in actively ferment- 

 ing or decomposing matter the respiratory activity of the micro- 

 organisms concerned (although not involving a consumption of free 

 oxygen) is very great. The rise of temperature in a hotbed is due 

 mainly to the respiratory activity of the Bacteria in the manure. 



Among the higher plants large flowers or inflorescences show the 

 most marked evolution of heat. In some large tropical Aracese and 

 Palms the difference in temperature between the interior of the 

 spathe and the outside air may amount to 10-12 C. 



Sulphur, Nitro, and Iron Bacteria 



In some Bacteria the necessary energy is supplied by oxidation, 

 not of carbon compounds, but of sulphur, nitrogen, or iron com- 

 pounds. . Thus Beggiatoa oxidizes sulphuretted hydrogen into sul- 

 phur and sulphuric acid; 'the Nitro-bacteria oxidize ammonia into 

 nitrous and nitric acid ; the Iron-bacteria oxidize ferrous into ferric 

 oxide. 



Anaerobic Respiration 



While normal plants, like animals, require free oxygen for respi- 

 ration, certain Bacteria (Anaerobes) can live in the absence of free 

 oxygen, and, indeed, some of them (e.g. Bacillus polypiformis) are 

 quickly killed by even small amounts of free oxygen. In the in- 

 terior of decomposing bodies all the uncombined oxygen is soon 

 exhausted by the growth of the Bacteria present, and they must be 

 able to live and grow in the absence of free oxygen. Indeed, the 

 strictly anaerobic forms do not begin their activity until the free 

 oxygen has been exhausted by their predecessors. 



In these anaerobic forms the necessary supply of energy is furnished, 

 not by the action of free oxygen, but by the chemical decomposition 

 of substances within the cell, resulting in the evolution in many 

 cases of large amounts of alcohol, lactic acid, butyric acid, etc., as 

 well as C0 2 and water. This form of respiration is often known as 

 " intra-molecular " respiration, and may also take place in plants 

 which normally are aerobic. 



GROWTH 



In unicellular plants cell-division at once results in the forma- 

 tion of two individuals, which immediately grow to the size of the 

 2i 



