RESPIKATION. 57 



everything has worked properly, the baryta water under the jar with the plant 

 will show the film of barium carbonate, while the other one will show none. 

 Respiration, therefore, takes place in a leafy plant as well as in germinating 

 seeds. 



134. Bespiration in fungi. — If several large actively growing mushrooms 

 are accessible, place them in a tall glass jar as described for letermining 

 respiration in germinating peas. In the course of twelve hours test with the 

 lighted taper and the baryta water. Respiration takes place in fungi as well 

 as in green plants. 



135. Bespiration in plants in general. — Respiration is general in all 

 plants, though not universal. There are some exceptions in the lower plants, 

 notably in certain of the bacteria, which can only grow and thrive in the ab- 

 sence of oxygen. 



136. Bespiration a breaking-down process. — We have seen that in res- 

 piration the plant absorbs oxygen and gives off carbon dioxide. We should 

 endeavor to note some of the effects of respiration on the plant. Let us 

 take, say, two dozen dry peas, weigh them, soak for 12-24 hours in water, 

 and, in the folds of a cloth kept moist by covering with wet paper or sphag- 

 num, germinate them. When well germinated and before the green color 

 appears dry well in the sun, or with artificial heat, being careful not to bum 

 or scorch them. The aim should be to get them about as dry as the seed 

 were before germination. Now weigh. The germinated seeds weigh less 

 than the dry peas. There has then been a loss of plant substance during 

 respiration. 



137. Detailed result of the above experiment to show that respiration is 

 necessary for growth. — The experiment was started at 9.30 a.m. on July 

 8, and the roots measured 20-2e,mvt. At 3 p.m. on the following day, 

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

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

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

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

 CO2 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 CO2. 



In one of the experiments the two jars were allowed to stand at the room 

 temperature for several weeks. At the end of that time the peas in the jar 

 containing air had grown until the vines reached to the top of the jar, and the 

 vines had branched and produced a number of green leaves. In the other jar 

 no growth took place. In fact the peas died. At this time the gas in both of 

 the jars was tested by lowering a lighted taper. In the jar with the growing 



