THE CARBOHYDRATE ECONOMY OF CACTI. 



By HERMAN AUGUSTUS SPOEHR. 



I. INTRODUCTORY DISCUSSION. 



The best evidence gained since the time of Sachs points to the conclusion 

 that sugars are the first products which accumulate in the process of the 

 photosynthesis of carbon compounds in the chlorophyllous cell. Thus, 

 sugars may be considered the starting-point for the synthesis of the tre- 

 mendous number of substances found in living things, both vegetable and 

 animal. What the sugar or mixture of sugars is which thus commands the 

 center of attention in the metabolism of plants and of almost all living 

 things is still a question of much dispute and uncertainty; nor does the 

 solution of this problem seem possible until we have gained more knowledge 

 of the transformations which the various sugars undergo in the cell, inde- 

 pendent of photosynthesis. It has long been known that in the leaf, under 

 circumstances, the polysaccharides are converted into the simpler sugars 

 and vice versa, by what appears to be the shifting of an equilibrium by 

 means of enzyme action. It is self-evident that a knowledge of these trans- 

 formations must be obtained before the problem of the first sugar syn- 

 thesized can be attacked. 



Not only in relation to the question of the immediate products of photo- 

 synthesis is the study of the carbohydrate equilibrium important, but also 

 to the question of metabolism. In a very large number of plants, especially 

 the higher ones, both the living and the lifeless matter consists in the main 

 of material of carbohydrate nature. The lifeless matter forms the walls, 

 vessels, supporting frame-work, and often a considerable amount of the 

 reserve food-material. Those portions of the plant in which the manifesta- 

 tions of life appear, as for instance the chromatin of the nucleus and the 

 protoplasm itself, contain a considerable quantity of carbohydrates, the life- 

 less being formed from the living and the living drawing upon the lifeless 

 for support. It is, however, a question whether the difference between the 

 living and lifeless is essentially one of chemical constitution. The idea that 

 the living substance or protoplasm is a complex compound of more or less 

 definite chemical constitution no longer seems tenable. Protoplasm, a 

 mixture of so many different substances, undoubtedly varies in composition 

 in different organisms. It is in all probability the study of the physical 

 and chemical properties of protoplasm as a colloidal mixture (such proper- 

 ties as imbibition of water, electrical charges, and surface phenomena) 

 which will yield the most illuminating results. 



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