RESPIRATION 15 



Within the limits in which normal respiration is possible, 

 plants, and hence their component cells, will supply them- 

 selves with adequate amounts of oxygen, an excessive pro- 

 portion suddenly supplied causing, in some plants, merely a 

 greater accumulation of oxygen, unaccompanied by greater 

 respiration, * in the cells ; in others, more rapid respiration 

 as indicated by higher temperature, etc. On the other hand, 

 sudden reduction of the amount of oxygen may cause a 

 diminution of the respiratory activity. 



So long as the general conditions for life continue in ade- 

 quate degree, there is no cessation of respiration in plants 

 or in animals. This is true of the resting forms buds, 

 bulbs, tubers although in them the rate of respiration is 

 much lower than in active forms. It is possible to force 

 these resting forms by various means into activity, but it 

 is not possible, after the}' mature, to continue the rate of 

 respiration which they possessed during their development. 

 The forming bud, bulb, or tuber is composed of cells ac- 

 tively working, needing much energy with which to work, 

 and respiring rapidly in order to secure this. With the ap- 

 proach of maturity of the parts, the work to be done, the 

 need of energy, and the rate of respiration, diminish, no 

 matter how favorable to continued activity the external 

 conditions may be. This decrease in respiration, and in the 

 other functions, is largely due to the influences of its envi- 

 ronment upon all the functions of the organism as a whole. 

 The organism prepares itself for the regularly recurring 

 periods of drought, heat, or cold ; one activity after another 

 is suspended accordingly. After a period of rest, it is possi- 

 ble to force these forms into activity even after the lapse of 

 much less than the usual time. Lilac branches, cut from the 

 bushes late in autumn, can be forced by Christmas time to 

 develop the flowers and leaves already formed. This forcing 

 is accomplished by placing the ends of the cut branches in 

 jars of water and keeping them in a warm, damp, not too 

 brightly lighted place. This experiment, familiar enough to 

 the florist, results in the resumption of active respiration 



* Pfeffer ? 8 Handbuch der Pflanzenphysiologie, 2te Auflage, Bd. I., p. 

 547, 1897. Eng. tranel. by Ewart, vol. I., p. 539, 1900. 



