METASTASIS. 183 



by the oxidation of some of the saccharine or amylaceous 

 substances in the plant, while the alkaloids with which they 

 are combined appear to have some relation to the nitrogenous 

 constituents of liie protoplasm, and ure possibly derived from 

 them. 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 which are formed instead 

 of the ordinary albuminoids, or the first results of the incip- 

 ient decay of the cells. 



240. Results of Metastasis. In the preceding para- 

 graphs it is seen that chlorophyll-bearing plants absorb 

 carbon dioxide and exhale free oxygen, the former being de- 

 composed 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. It is further 

 seen that oxygen is absorbed and carbon dioxide evolved, as 

 results of certain metastatic processes which take place in 

 any tissues, whether possessing chlorophyll or not, and inde- 

 pendently of the presence or absence of sunlight. In the 

 sunlight the absorption of carbon dioxide to supply assimila- 

 tion is so greatly in excess of its exhalation as a result of 

 metastatic action, that the latter is unnoticed. In dark- 

 ness, however, when assimilation is stopped, the exhalation 

 of carbon dioxide becomes quite evident. So, too, with 

 oxygen ; in the sunlight the excess of its evolution is so 

 great over its absorption 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 ordinary 

 plants which are wanting in chlorophyll, as flowers and many 

 fruits, deport themselves in this regard exactly as chloro- 

 phyll-bearing organs do in darkness. 



