RESPIRA TION. 



233. Eespiration in fungi. If several large actively growing mushrooms 

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

 respiration in germinating peas. In the course of 1 2 hours test with the 

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

 well as in green plants. 



234. Respiration 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 absence of oxygen. 



235. Respiration 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 burn 

 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. 



236. Fermentation of yeast. Take two fer- 

 mentation tubes. Fill the closed tubular parts 

 of each with a weak solution of grape sugar, or 

 with potato decoction, leaving the open bulb 

 nearly empty. Into the liquid of one of the 

 tubes place a piece of compressed yeast as large 

 as a pea. If the tubes are kept in a warm place 

 for 24 hours bubbles of gas may be noticed 

 rising in the one in which the yeast was placed, 

 while in the second tube no such bubbles appear, 

 especially if the filled tubes are first sterilized. 

 The tubes may be kept until the first is entirely 

 filled. with the gas. Now dissolve in the liquid 

 a small piece of caustic potash. Soon the 

 gas will begin to be absorbed, and the liquid 

 will rise until it again fills the tube. The gas 

 was carbon dioxide, which was chiefly pro- 

 duced during the anaerobic respiration of the 

 rapidly growing yeast cells. In bread making 



, this gas is produced in considerable quantities, and rising through the 

 dough fills it with numerous cavities containing gas, so that the brea>~ 

 "rises." When it is baked the heat causes the gas in the cavities to ex- 



Fig. 107. 



Fermentation tube with 

 culture of yeast. 



