136 



PLANT PHYSIOLOGY 



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the question whether, in the best marked of such cases, the car- 

 bon dioxide can be released if no oxygen at all is present, which 

 presents this problem: 



Can seeds 0} abnormally high respiratory ratio release carbon 

 dioxide without presence 0} any oxygen? 



This may readily be determined by placing the seeds in question 

 under conditions favorable for respiration, except that all oxygen is 

 excluded. 



Experiment. Fill the tube, and half fill the reservoir, of an 

 anaerobic culture vessel with clean mercury; take two or three fully 

 soaked small Peas, remove their seed-coats (so that air may not be 

 enclosed), plunge them (with forceps) under the mercury, and shake 

 them free of air, then release them under the tube, when they will 

 rise to its top and lie completely enclosed in the mercury. Give favor- 

 able conditions for respiration, and when gas formation has ceased, 

 or nearly (after two or three days), apply the carbon-dioxide test by 

 slipping a small piece of solid caustic potash into the tube. 



Anaerobic Culture Vessels. These may be of much elaboration for 

 special studies (compare Detmer, 264), or may be much simpler and still 



efficient for our present use. They may 

 consist of chambers in which the seeds 

 lie in pure hydrogen gas (later analyzed 

 for the carbon dioxide), or a Torricellian 

 vacuum (Detmer, 275), or some form 

 of "fermentation tube," of which the 

 Smith form, commonly used in this 

 country, has rather too small a neck 

 for the insertion of the potash, an 

 objection which does not apply to the 

 KiJHNE form (figured by Detmer, 263) 

 But equally efficient, while readily adapted 

 from common appliances, is the arrange- 

 ment figured herewith (Fig. 35), consist- 

 ing of a small test-tube supported 

 inverted over a small glass mortar or 

 other vessel containing mercury. If it 

 were desired to make the study quanti- 

 tative, a graduated test tube could be 

 used, and the seeds could be with- 

 drawn by very fine wires previously 

 attached to them and extending through the mercury. 



The formation of carbon dioxide anaerobically, that is, in 

 absence of free oxygen, shown by this experiment, suggests an 



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Fig. 35. — Anaerobic culture 

 vessel, using mercury; xi- 



