236 RESPIRATION 



animals originates in a similar manner : when the physiological 

 oxidation is prevented growth ceases, the streaming movement 

 of the protoplasm within the cells is stopped, and the move- 

 ments of the leaves, roots, stems and other organs of plants are 

 suspended. 



In all cases heat is produced during respiration, and in warm- 

 blooded animals it is easily perceived. In plants, oxidation is 

 generally much less energetic than in animals, and the heat 

 produced is so slight that no difference in temperature can be 

 detected between green plants and that of the air surrounding 

 them. Moreover, in ordinary green plants exposed to the air, 

 the cooling effect of transpiration masks any slight rise in tem- 

 perature due to respiration. However, when actively germinat- 

 ing seeds or rapidly expanding flowers and buds are heaped 

 together, a rise of two or three degrees above that of the 

 atmosphere may be readily observed, by placing the bulb of 

 a thermometer among them. 



The amount of respiration is dependent on external and 

 internal conditions, and in different parts of the same plant 

 the activity of the process is not the same. In all young actively 

 growing parts rich in protoplasm, such as germinating seeds, 

 expanding buds and flowers, respiration is vigorously carried on, 

 and the same is noticeable in injured cut portions of plants. 

 In dormant bulbs, tubers and buds little or no respiration is 

 observable. In dry seeds respiration seems to be entirely 

 suspended, and many have been kept for twelve months in a 

 vacuum, and in nitrogen and other gases under conditions which 

 render respiration impossible, yet after such treatment the seeds 

 germinated freely. 



At freezing-point and a degree or two below it, where growth 

 is stopped, respiration may frequently be detected. With in- 

 creasing temperature there is a steady increase in the amount of 

 respiration up to the point where death takes place, and the 

 process stops suddenly. 



