2f8 



RESPIRATION 



respiration continues for a time, but finally stops. This 

 proves that the absorption of oxygen increases respiration. 

 (iii.) Temperature. A rise in temperature up to a certain 

 extent favours respiration. This can be proved by keeping 

 germinating seeds in a, cold place, when they will respire slowly, 

 (iv.) Rapidly -growing parts respire vigorously. Any circum- 

 stances (fall in temperature, stopping supply of oxygen) calcu- 

 lated to stop growth, retard respiration. This is really putting 

 " the cart before the horse," because the stoppage of growth 

 is largely caused by the arrest of respiration, not vice versA. A 

 passive resting-seed or tuber respires very slowly indeed, 

 but when growth commences, its respiration is rapid, (v.) Only 

 living parts of plants respire. This is the most important fact 

 of all, though not easy to prove. We can illustrate it by 



killing moistened 

 seeds by means of 

 boiling water, and 

 comparing their 

 effect on the air 

 in a closed bottle 

 with the effect pro- 

 duced by germin- 

 ating seeds which 

 are living. 



Respiration 

 causes a libera- 

 tion of heat from 

 the plant. — If a 

 thermometer be 

 plunged amongst 

 a number of ger- 

 minating seeds or 

 young flowers, the 

 mercury will rise, 

 thus showing that the seeds are warmer than the surrounding 

 general atmosphere. If the seeds be killed, there will be no 

 appreciable change in the level of the mercury of the thermo- 

 meter, thus proving that the rise of temperature is dependent 

 on the parts being alive. In general, any conditions which 

 retard respiration will cause the rise in temperature to be 

 smaller. 



Fig. 248.— Apparatus to show the rise of temperature 

 during respiration, A thermometer-bulb is surrounded by 

 germinating peas, which are in a glass funnel. Outside is 

 a reversed box, of wood or cardboard, through a hole in 

 which the thermometer-tube passes. 



