CHAPTER XXIX 



RESPIRATION 



When seeds germinate in a dark room, the total weight of the develop- 

 ing seedlings will increase for a number of dajs, but their dry weight will 

 consistentl}' decrease. This can be shown by calculating the dry weight of 

 the seeds at the time of planting from a water content determination of 

 other seeds from the same batch, and determining the dry weight of the re- 

 sulting seedlings after they have been allowed to develop for several weeks. 

 For example, Boussingault found many years ago that the dry weight of ten 

 pea seedlings allowed to develop in the dark was 1.076 g. while the dry 

 weight of the original seeds was 2.237 g. In other words 1.161 g. or 52 per 

 cent of the dry substance initially present in the seeds disappeared during the 

 course of the experiment. By chemical analysis it can be shown that the 

 loss of dry weight of seedlings growing in the absence of light is due entirely 

 to the disappearance of a portion of the stored foods in the seed. The gain 

 in total weight of such seedlings is due to the absorption of water which 

 occurs during the early stages of germination in quantities far surpassing any 

 loss of dry weight due to the disappearance of foods. The quantity of mineral 

 salts absorbed by young seedlings in the course of a week or two is usually 

 too small to have any appreciable effect upon either their dry or total weight. 



If seedlings developing in the dark are enclosed in a chamber which is 

 so constructed that a slow, continuous stream of air can be passed through 

 it, and frequent analyses made of the air, it can be demonstrated that oxygen 

 is continually diffusing into the seedlings and carbon dioxide is continually 

 diffusing out of them. 



Furthermore, if such seedlings are enclosed in a calorimeter, and other 

 suitable precautions taken which will be described later, it can also be shown 

 that heat — which is one kind of energy — is continuously escaping from them. 



All of these phenomena — disappearance of food resulting in a decrease in 

 dry weight, absorption of oxygen, evolution of carbon dioxide, and liberation 

 of energy — are different external manifestations of the process of respiration 

 which occurs, not only in germinating seeds and seedlings, but in almost every 

 living cell. 



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