RESPIRA TION. 



57 



8, and the roots measured 20-25/nm. At 3 p.m. on the following day, 

 29 hours after the experiment was started, the roots were examined. Those 

 in the C0 2 gas had not grown perceptibly, while those in the jar containing 

 air had increased in length lo-iomm. In fig. 48 are represented two of the 

 peas, drawn at the close of the experiment, a represents the one from the 

 C0 2 jar which had the longest root, b represents one of the longer ones from 

 the jar with air. Here we have also a good comparison with the peas 

 grown in the mercury tubes, since those in the tube which contained some 

 air were checked in growth to a considerable extent, by the accumulation of 

 carbon dioxide in the small space in the tube, and did not represent a fair 

 comparison of root growth in air and in CO.,. 



138. Another way of performing the experiment. — If we wish we may 

 use the following experiment instead of the simple one indicated above. Soak 

 a handful of peas in water for 1 2-24 

 hours, and germinate so that twelve 

 with the radicles 20-2$m»i long 

 may be selected. Fill a test tube 

 with mercury and carefully invert 

 it in ■■< vessel of mercury so that 

 there will be no air in the upper end 

 (there may be a small vacuum). 

 Now nearly fill another tube and 

 invert in the same way. In the 

 latter there will be some air. Re- 

 move the outer coats from the peas 

 so that no air will be introduced in 

 the tube filled with the mercury, 

 and.insert them one at a time under 

 the edge of the tube beneath the 

 mercury, six in each tube, having 

 first measured the length of the 

 radicles. Place in a warm room. 

 In 24 hours measure the roots. 

 Those in the air will have grown 

 considerably, while those in the 

 other tube will have grown but 

 little or none. 



The apparatus to demonstrate 

 this was set up at 10 a.m. on July 

 8, 1897. The tube filled with mercury was supported by a clamp, while 

 the tube which was only partly filled was stable enough to support itself 

 until by the accumulation of gas nearly all the mercury moved out, when 

 it was weighted down, 



Fig. 50. 

 Experiment to show that growth takesplace 

 more rapidly in presence of oxygen than in ab- 

 sence of oxygen. At the beginning of the experi- 

 ment the two tubes in the vessel represent the 

 condition at the beginning of the experiment. 

 At the close the roots in the tube at the left were 

 longer than those in the tube filled at the start 

 with mercury. The tube outside of the vessel 

 represents the condition of things where the peas 

 grew in absence of oxygen ; the carbon dioxide 

 given off has displaced a portion of the mercury. 

 This also shows intramolecular respiration. 



