EESPIEATION 123 



during their winter suspension of development, but in 

 such cases the gaseous interchange is reduced to a mini- 

 mum. In growing shoots or germinating seeds in which 

 vital processes such as the growth of protoplasm are going 

 on rapidly, and life is very active, it reaches a maximum. 

 In ordinary adult leaves and branches the activity of 

 respiration is intermediate between the other two condi- 

 tions. It is more intense, again, in the floral organs during 

 the time of their maturation. We may say in general 

 terms, wherever protoplasm is abundant, and the chemical 

 processes connected with the manifestation of its life are 

 going on most vigorously, there respiration is most active. 

 It is connected especially with the vital processes, and is 

 not associated directly with the presence of food materials. 

 A proof of this is afforded by an estimation of the activity 

 of respiration in seedlings, which, in the case of wheat, has 

 been found to increase steadily for about a fortnight, and 

 then to decline. Further evidence is afforded by the fact 

 that if seeds are thoroughly dried they do not respire. In 

 this condition the protoplasm is completely quiescent, so 

 far as we can ascertain. If, however, only a little water is 

 supplied to them, which, as we have seen in an earlier 

 chapter, is a condition necessary to set up changes in the 

 protoplasm, respiration commences, and increases as the 

 proportion of water present rises up to a certain limit. 



When the respiratory processes are carefully measured 

 and compared with the weight of the organism, it is found 

 that under appropriate conditions they are more intense in 

 plants even than in warm-blooded animals. The respiratory 

 activity is as great in many seedlings as it is in the human 

 body, provided that both are maintained at the same 

 temperature. There is, however, a very great variability in 

 this respect, and the maximum activity is never maintained 

 very long in any particular plant. As maturity succeeds to 

 development its amount falls materially, being marked at 

 or near the original rate only in the regions of the active 

 meristems. 



