Respiration, Aeration, and Fermentation 287 



dried, active respiration begins. The curve of CO 2 ex- 

 cretion depends upon various external conditions, but a 

 maximum is generally obtained by the time shoot and root 

 are fairly elongated, after which there may be a rapid or 

 gradual decline until the seedling is well developed. The 

 curve shown (Fig. 70) is made up from data given by 

 Mayer, and it shows the results with seedlings of wheat 

 at a temperature of 23.8 C. 



This curve may be taken as merely a sample of the res- 

 piratory rate during germination, although the curves for 

 other seed may not be closely conformable. Frequently the 

 rate of respiration for germinating seeds is, with respect to 

 weight, about equivalent to that of man, generally given 

 as about 1 per cent of the body weight for 24 hours. Seeds 

 which germinate rapidly may, however, lose, under favor- 

 able conditions, one third of their dry- weight during a 

 period of 10 days, which is an average of about 3 per cent 

 per day. In such cases, therefore, the intensity of respira- 

 tion is relatively greater than for many warm-blooded 

 animals. 



As the embryonic tissues in the plant are relatively 

 reduced, the respiratory ratio will fall, so that well-de- 

 veloped plants, or those growing slowly, will show, with 

 respect to body weight, an exceedingly low ratio. Plants 

 or organs passing into a resting stage will fall to a minimum 

 which, in the case of dry seeds and well-protected bulbs, 

 may approximate zero. On the other hand, opening 

 flower-buds may show a high respiratory activity, often 

 relatively greater than at the time of germination. 

 According to Pfeffer, rapidly growing bacteria may con- 

 sume oxygen at a rate 200 times as rapid as required by 



