Ch. IV, 8] RESPIRATION OF PLANTS 169 



may be proven by suitable methods, as explained with our 

 picture (Fig. 117). It is this same respiration heat, intensi- 

 fied and regulated, which yields the "blood heat" of animals. 

 It will now be worth while to summarize the contrast be- 

 tween photosynthesis and respiration, as is possible in a 

 table. 



Photosynthesis Respiration 



Occurs only in green plants Occurs equally in all plants 



and animals 

 Takes place only in the chloro- Takes place in all living 



phyll grains protoplasm 



Proceeds only in light Proceeds in both light and 



darkness 

 Constructs food Destroys food 



Increases weight Lessens weight 



Absorbs carbon dioxide Releases carbon dioxide 



Releases oxygen Absorbs oxygen 



Forms grape sugar from car- Reduces grape sugar to car- 

 bon dioxide and water bon dioxide and water 

 Stores energy Releases energy 



Thus respiration destroys the product of photosynthesis, 

 but in the process develops the driving power for plant and 

 animal life. 



There is a form or phase of respiration so important as 

 to demand special treatment, and that is fermentation. 

 If some Yeast (which is a unicellular microscopic plant, to 

 be fully described in Part II of this book), in the form of 

 ordinary compressed Yeast, be placed in a flask with water 

 and sugar, and stood in a warm place, within a few minutes 

 the mixture begins to "work" or ferment, producing many 

 fine bubbles which rise through the liquid and form a froth at 

 the top. If, from this flask a bent outlet tube be led under 

 limewater (Fig. 118), through which the escaping gas can rise, 

 then the limewater will turn very milky, proving the gas 

 to be carbon dioxide. After fermentation has ceased, the 





