114 PHYSIOLOGY. 



be no air in the upper end. N"o\v nearly fill another tube and invert in the 

 same way. In the latter there will be some air. Remove the outer coats 

 from the peas so that no air will Ijc 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. 



230. Anaerobic respiration. — The last e.xperiment is also an excellent 

 one to s\v>v; anaerohk respiration. In the tube filled with mercury so tha 

 when inverted there will be no air, it will Ije seen after 24 hours that a gas 

 has accumulated in the tube which has crowded out some of the mercur\\ 

 With a wash bottle which has an exit tube properly curved, some water 

 may Vjc introduced in the tube. Then insert underneath a small stick ol 

 caustic potash. This will form a solution of potash, and the gas will be 

 partly or completely absorbed. This shows that the gas was carbon di- 

 oxide. This evolution of carbon dioxide bv living plants \\'hen there is no 

 access of o.xygen is anaerobic respiration (sometimes called intramoleculai 

 respiration). It occurs to a marked extent in the yeast plant. 



231. Energy set free during respiration. — From what we have learned of 

 the exchange of gases during respiration we infer that the jilant loses carbon 

 during this process. If the process of respiration 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 ]ilace. 



It can be shown b^■ an exjteriment that during respiration there is a 

 slight elevation of the temperature in the plant tissues. The plant then 

 gains some heat (luring respiraticjn. F.nerg^• is also manifested bv growth. 



232. Respiration in a leafy plant. — We may take a potted plant which 

 has a well-develij]ied leaf surface andjilace it under a tightl\' fitting liell jar. 



Under the bell jar there also should be placed 

 a small \'essel containing bar}'ta water. .\ sim- 

 ilar apparatus should be set uji, but \\ath no 

 ptlant, to serve as a check. The ex]ieriment must 

 be set uj' in a room which is not fretpiL-nted bv 

 persons, or the carbon dioxide in the roctm from 

 respiration Avill \'itiate the experiment. The bell 

 jar conlaining the plant slmuld be {civered with 



a black I loth to prL'\'(.-nt carbon assimilation. In 

 Fib- 106. , , , . ,1-1 



T. . r Ti V f the coursi.- o 10 or 12 hours, 1 e\er\'l nng has 



lest for lilneration nt car- - -^ 



bnn dioxide from leafv plant worked ]iroperh-. the barN'ta water under the iar 



during respiration. Baryta . , , ■,, , , -1 r , ■ 



water in smaller vessel. wUh the |ilantwill show the film ol banumca-- 



'^^''^^■^ bonate, while the other one will show none. Res- 



piraticjn, therefore, takes place in a leaf}' jilatit es \\'ell as in germinating ^eeuU 



