84 BOTANY. 



167. From the fact that the alkaloids are formed more 

 abundantly in those tissues which have passed the period 

 of their greatest activity, it may be surmised that they are 

 either compounds of a lower grade than the ordinary albu- 

 minoids, or the first results of the incipient decay of the 

 cells. 



168. Results of Assimilation and Metastasis. — In the pre- 

 ceding paragraphs we have found that chlorophyll-bearing 

 plants absorb carbon dioxide and exhale free oxygen, the 

 former being decomposed in the chlorophyll-granules in 

 sunlight, and the oxygen being set free as a consequence. 

 In other words, the absorption of carbon dioxide and the 

 exhalation of oxygen are connected with the process of 

 assimilation. 



169. Now, it may be shown that oxygen is absorbed and 

 carbon dioxide evolved, as results of certain metastatic 

 processes which take place in any tissues, whether possess- 

 ing chlorophyll or not, and independently of the presence 

 or absence of sunlight. In the sunlight the absorption of 

 carbon dioxide to supply assimilation is so greatly in excess 

 of its exhalation, as a result of metastatic action, that the 

 latter is unnoticed. In darkness, however, when assimila- 

 tion is stopped, the exhalation of carbon dioxide becomes 

 quite evident. 



170. So, too, with oxygen: in the sunlight the excess of 

 its evolution from assimilation is so great over its absorp- 

 tion for metastasis that the latter was long unknown; but 

 in the absence of light its absorption becomes manifest. 

 Parasites and saprophytes, as well as those parts of ordi- 

 nary plants which are wanting in chlorophyll, as flowers 

 and many fruits, deport themselves in this regard exactly 

 as chlorophyll-bearing organs do in darkness. 



