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, ete. 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 
