9 6 



BOTANY. 



169. Oxygen is necessary for growth. — In 24 hours examine and note 

 how much growth has taken place. It will be seen that the roots have elon- 

 gated but very little or none in the first jar, while in the second one we see 

 that the roots have elongated considerably, if the experiment has been carried 

 on carefully. Therefore in an atmosphere devoid of oxygen or an excess of 

 carbon dioxide, very little growth will take place, which shows that normal 

 respiration with access of oxygen is necessary for growth. 



170. Energy set free during respiration. — From what we 

 have learned of the exchange of gases during respiration we 



infer that the plant loses carbon during 

 this process. If the process of respira- 

 tion is of any benefit to the plant, there 

 must be some gain in some direction 

 to compensate the plant for the loss of 

 carbon which takes place. 



It can be shown by an experiment 

 that during respiration there is a slight 

 elevation of the temperature " in the 

 plant tissues. The plant then gains 

 some heat during respiration. We 

 have also seen in the attempt to grow 

 seedlings in the absence of oxygen that very little growth takes 

 place. But when oxygen is admitted growth takes place 

 rapidly. The process of respiration, then, also sets free energy 

 which is manifested in one direction, by growth. 



Fig. 75- 

 Pea seedlings ; the one 

 at the left had no oxygen 

 and little growth took 

 place; the one at the right 

 in oxygen and growth was 

 evident. 



Demonstration 27. 



171. To set np the apparatus for demonstrating respiration. — Soak a 

 double handful of peas for 12 to 24 hours in an abundance of cool water. 

 Prepare a small quantity of baryta water, a saturated solution, and filter some 

 into a short wide vial. Take a glass cylinder about 35«re high by ^cm in 

 diameter. Select a perforated rubber cork to fit very tightly when crowded 

 part way in the open end of the cylinder. Prepare a long S manometer by 

 bending a glass tube which is about one and one-half meters long by (mfm 

 inside diameter, into the form shown in figure 76. Put mercury into one 

 end of the manometer as shown in the figure, and if it is desired to show the 



