RESPIRATION 91 



mangroves (e.g. the black mangrove of Florida, Avicen- 

 nia nitida). 



137. Respiration consists primarily in the breaking up 

 of the complex molecules of certain organic compounds 

 (chiefly carbohydrates or even the carbohydrate portions 

 of protoplasm molecules) into simpler compounds. This 

 releases a large amount of energy much of which becomes 

 available for the use of the plant. Since all living parts 

 of the plant require energy, respiration will be found to 

 take place in all parts. The intensity of the respiration 

 varies with many factors, viz. the amount of food avail- 

 able that can be broken down into simpler compounds, 

 the availability of oxygen, the amount of water, the 

 temperature, etc. To what extent the protoplasm itself 

 can regulate the occurrence of this process, if the other 

 conditions are fulfilled, is uncertain. 



138. Part of the energy set free in respiration is 

 exhibited in the form of heat. This is especially notice- 

 able where rapid growth and rapid respiration are oc- 

 curring as in large flower buds, fruiting bodies of large 

 fungi, etc. In ordinary parts of plants the radiating 

 surface is great enough to keep the plant cool so that the 

 heating is not noticeable. In the case of wet leaves, hay, 

 manure, etc., the heat produced by the respiratory proc- 

 esses of the fungi and especially the bacteria present 

 leads in some cases to the kindling of some of the easily 

 inflammable substances produced so that it is a frequent 

 occurrence for hay, especially moist alfalfa hay, and 

 manure to catch fire. 



139. It has been shown that there are two distinct 

 stages in respiration which follow one another so closely 

 in most cases that they appear as one. These are the 

 anaerobic and aerobic stages. Certain bacteria and 

 yeasts show only the first stage. In this stage no oxygen 



