RESPIRATION 293 



ture of the clusters and the outside air are commonly observed, 

 while in the spadices of some aroids differences of 30° C. have 

 been noted. All this heat eliminated from seeds and unfolding 

 buds comes, in the main, from respiration; but it must not be 

 forgotten that other chemical changes which go on within the 

 plant, such as the enzymic hydrolysis of carbohydrates, as well 

 as certain physical phenomena, such as imbibition, are accompanied 

 by the liberation of heat and may account for a fraction of the 

 heat produced. 



Decrease in Dry Weight. — Since respiration results in the 

 oxidation of carbon compounds present in the plant with the 

 elimination of the carbon dioxide produced, a decrease in dry 

 weight is to be anticipated. If a seedling is grown in the dark, 

 the bulk of the young seedling may be many times that of the seed, 

 but if all the water is driven off and the dry weight alone taken, 

 it will be found that the plant although gaining in bulk has lost 

 appreciably in dry weight. The evaporation of the water pro- 

 duced in the reaction will also cause a loss of weight. 



Seeds containing fat or oils do not lose as much dry weight 

 during germination as those which store their reserves in the 

 form of starch and sugar. It has even been stated that flaxseed 

 increased in dry weight, but this has been definitely disproved. 

 Such oily seeds lose so much less dry weight than other seeds be- 

 cause during germination the fat is changed to carbohydrates 

 before it is respired, and in making this change a great deal of 

 oxygen is added to the fatty material. The gain in oxygen through 

 this transformation of fats nearly equals the loss in weight through 

 respiration, with the result that the net balance is almost as great 

 as that of the original material. 



While carbon dioxide and water are the principal products of 

 respiration, in some cases, succulents, for instance, respiration is 

 incomplete and organic acids only are formed. These are thought 

 to serve as reserves of carbon dioxide which can later be used in 

 photosynthesis. In the bladder floats of some of the marine algae 

 (Nereocystis), carbon monoxide has also been found, but this is a 

 very exceptional respiration product. In this case the gas may 

 reach as high as 12% of the included gases but it is found only 

 when the plant is supplied with oxygen, indicating that it is con- 

 nected with respiration rather than with other processes like photo- 

 synthesis. 



