180 BOTANY. 



them from those of assimilatiou, the term Metastasis* has 

 been applied. 



It is even more difficult to give anything like a complete 

 account of the processes of metastasis than of those of assim- 

 ilation ; all that can be done is to indicate the general nature 

 of the chemical changes which are best known. 



234.— Transformation of Starch. In darkness the starch 

 which had previously formed in the chlorophyll-bodies at 

 once undergoes changes which render it soluble, allowing it 

 to diffuse to other parts of the plant with great freedom. 

 The nature of these changes appears to vary somewhat in 

 different plants, but they consist essentially in the transform- 

 ation of the insoluble starch into a chemically similar but 

 soluble substance. Glucose (C^, H,, 0, J, inulin (C,, H^, 0„), 

 and cane sugar (0,, H,^ 0„) are the more common of the 

 soluble substances so formed, and one or other of these may 

 frequently be detected in the adjacent cells after the disap- 

 pearance of the starch from the chlorophyll. 



235.— The Nutrition of Protoplasm. These diffusing as- 

 similated matters are imbibed by the protoplasm of the living 

 tissues, and constitute its most importa^^t food. In connec- 

 tion with the nitrates and sulphates, also imbibed, they 

 furnish the materials for the increase of protophismic sub- 

 stance in growing cells. The exact changes which take 

 place in the formation of protoplasm are unknown, but it is 

 probable that a portion of the soluble assimilated matter 

 (glucose, inuline, etc.) is broken up by the action of oxygen 

 into carbon dioxide and one of the organic acids {e.g., oxalic 

 acid) ; and the latter, by replacing the acids in the sulphates 

 and nitrates, may set free the sulphur and nitrogen necessary 

 to the formation of protoplasm. The occurrence of crystals 

 of calcium oxalate in the tissues of many plants rather indi- 

 cates the probability of this or a similar series of reactions. 



* Literally "to place in another way," from the Greek fiera beyond, 

 or over, and lardvai,, to place. We owe the present application of the 

 word to Professors Bennett and Dyer, who used it as the equivalent 

 of the German " Stoffwechsel " in their English translation of Sachs' 

 " Lehrbuch." 



