16 PLANT PHYSIOLOGY 



after a period of tardy respiration shorter than usual; it 

 does not continue the respiratory and other activities at the 

 rate prevailing during the formation of the parts. 



Respiration is a process conducted and regulated by the 

 living protoplasm of the cells. It will not go on indefinitely 

 and independently however favorable the physical conditions 

 may be. It can be artificially increased only by stimulat- 

 ing the protoplasm to greater activity ; it will be increased 

 whenever the protoplasm becomes more active. The respira- 

 tion of plants and plant-cells can be artificially reduced only 

 by reducing the general activity of the living protoplasm. 

 This may be accomplished by the same means as the animal 

 physiologist employs — by applying a local or general anaes- 

 thetic, by lowering the temperature, by preventing move- 

 ment, etc. In most plants and plant parts the forced cessa^ 

 tion of normal respiration immediately precedes, and is 

 itself the cause of, death. In certain plants — for example, 

 germinating peas — intramolecular respiration* may tem- 

 porarily take its place; in certain others — for example, 

 anaerobic bacterial — intramolecular respiration is the nor- 

 mal mode. 



Normal respiration cannot, however, be entirely suspended 

 in plants or plant parts without profound changes taking 

 place which sooner or later will result in death. The reduc- 

 tion of normal respiration to an extremely low rate, if not 

 its entire suspension, unaccompanied by any other means of 

 obtaining energy, regularly takes place in the ripe seed, but 

 only when the cells composing the seed lose the water which 

 is an essential constructive constituent of living proto- 

 plasm. 



In warm-blooded animals the object of respiration is two- 

 fold — the maintenance of a certain (normal) body-tempera- 

 ture and the production of energy for doing work. In cold- 

 blooded animals and in plants the object of respiration is 

 solely the latter. The average body-temperature of plants 

 is in general nearly the mean daily temperature of their 

 environment, and it will vary within certain limits accord- 

 ingly. The variation in the body-temperature of plants will 

 * See page 27. t See page 26. 



