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, 
