164 A TEXTBOOK OF BOTANY [Ch. IV, 8 



the seeds is in fact respiration, identical in all essentials 

 with that familiar in animals. 



If, now, other plant parts be placed in the respiroscope 

 chamber, — growing bulbs, roots, buds, flowers, fruits, leaves, 

 stems, — in fact any growing plant parts, and if the same 

 tests and analyses as before be applied, then the general re- 

 sult is always the same. It is true, there are cases in which 

 oxygen seems to be absorbed without release of carbon 

 dioxide, and cases in which carbon dioxide seems to be 

 released without absorption of oxygen, with all intermediate 

 gradations. These exceptions, however, from the point of 

 view of respiration, are not real, for in the former case the 

 carbon dioxide is known to be retained and used in forma- 

 tion of special substances, and in the latter the oxygen is 

 taken, not from the air, but from compounds composing the 

 / plant tissues themselves. And here is one further point of 

 7 the first importance, fully proved by respiroscopes. Respira- 

 tion occurs in general not only in tissues which are growing, 

 but in all tissues which are alive. In brief, respiration is 

 found to occur in all living and working parts of plants and 

 animals alike. Its amount depends, as a rule, upon the 

 activity of the parts, being directly proportional thereto. 



But what of green leaves, which were earlier shown to 

 perform an opposite process in their photosynthesis, absorb- 

 ing carbon dioxide and releasing oxygen? If, with green 

 leaves in the chamber, the respiroscope be kept in the light, 

 then indeed no carbon dioxide shows in the test ; but if the 

 instrument be kept in the dark, then that gas is yielded 

 abundantly. This does not mean that respiration stops in 

 the light, but only that then it is surpassed by photosyn- 

 thesis, which for the same area of leaf is, on the average, 

 v about twelve times more active than respiration. This fact 

 explains why photosynthesis, even though in progress only 

 a part of the time, can purify the air, despite the unceasing 

 respiration of both plants and animals. 



Respiration is little affected by darkness or light. Ac- 



