302 Plant Physiology 



control flask (containing killed seed) which would indicate con- 

 tamination, necessitating the close of the experiment. Plot 

 curves of the temperature conditions in the two flasks. 



Oxygen and growth. - - After introducing seeds (Fig. 75) 

 attached to a cork into A (shown at the left), fill AB with 

 water recently boiled and recooled. Close stop-cock N, invert, 

 connect with C (a tube with air only) and with D (a tube con- 

 taining potassium pyrogallate (see p. 221). Shake the series 

 (stopcock O open) until the oxygen is absorbed, close O, im- 

 merse vertically the OD end of the series into boiled, cool 

 water, disconnecting D, and opening O. temporarily, to relieve 

 (by inflow of water) the negative tension due to the absorption 

 of oxygen. Close O, remove the apparatus from the water, 

 open N, permitting the oxygen-free air to escape into A 

 displacing water. Then close N, detach the parts below the 

 latter, and place the AB part (as shown at the right) under 

 temperature conditions favorable for growth. Compare at 

 intervals the growth with seeds similarly placed in an open tube. 



Fermentation of sugars. - - Properly nil two fermentation tubes 

 (preferably the Kiihne form) with a 10 per cent sugar solution 

 (fresh) of each of the following : glucose, sucrose, and lactose. 

 In each tube insert a fragment of pressed yeast, plug the mouth 

 lightly with cotton, and in 24 hours or more compare the pro- 

 duction of gas caught in the closed arm. Insert in those showing 

 gas a stick of caustic potash and explain the results. 



For experiments such as the above, continued so short a time, 

 it is unnecessary to supply mineral nutrients, nor are sterilization 

 precautions necessary. 



Alcoholic fermentation. - - Prepare 500 cc. of a modified Pasteur 

 solution to contain the following : - 



Glucose 75 grams 



Ammonium tartrate 5 grams 



Potassium di-hydrogen phosphate 1 gram 



Calcium chlorid 5 gram 



Magnesium sulfate 5 gram 



Water 500 cc. 



