THE VITAL PHENOMENA OF CELLS 



23 



centrosome, by division of preexisting trophoblasts. These structures generate 

 within themselves the chlorophyll. 



The property of plants discovered by Ingenhousz (1779), Senebier (1782- 

 1800)., and Th. de Saussure (1804), of reducing carbon dioxide, depends upon 

 this chlorophyll. The reduction takes place under the in- 

 fluence of the sun's rays, and starch appears as the first 

 visible product of the resulting synthesis. It is deposited 

 in the chlorophyll bodies in the form of small, highly re- 

 fractive granules (Julius Sachs, 1862). At the same time 

 the plant gives off the oxygen set free by the reduction 

 of carbon dioxide, and if it grows in a closed room the 

 quantity of C0 2 in the confined air constantly decreases, 

 while the quantity of 2 is correspondingly increased. 



Starch serves as the starting point for all further syn- 

 thetic processes in the plant body. By its cleavage and 

 hydration different kinds of sugars are produced, and, 



this being the form in which 

 carbohydrates are transported, 

 they are of great importance in 

 the further synthetic processes 

 within the plant body. Vege- 

 table oils are also formed from 

 starch; and it participates 

 finally in the synthesis of pro- 

 teids in plants. 



Besides the elements found 

 in starch (carbon, hydrogen 

 and oxygen), proteids contain 

 nitrogen and sulphur (some 

 also phosphorus). The plant 

 obtains these elements from 

 the soil principally in the form 

 of nitrates, sulphates, phosphates and ammonia 

 compounds. It obtains on the other hand only an 

 insignificant part of its nitrogen from the ammonia 

 and nitric acid in the air. The nitrogen, sulphur 

 and phosphorus are liberated from their compounds 

 by processes of reduction and they together with 

 the elements contained in starch are synthetized 

 into proteids. It is very probable that the amino 

 acids and their amides e. g., asparagin (amino- 

 succinamic acid, C 4 H 8 N" 2 3 ) represent intermedi- 

 ate stages in this synthesis ; but how such processes 

 take place we do not yet know. Finally from the pro- 

 teids thus formed, living protoplasm is constructed. 

 Certain plants are able to absorb free atmospheric nitrogen and to com- 

 bine it into organic compounds. A species of bacterium, Clostridium Pas- 

 teurianum, which lives in the soil, is an example (Winogradsky). Kriiger 



FIG. 17. This leaf, 

 which, in the liv- 

 ing condition, had 

 been partially cov- 

 ered with a strip 

 of tin foil, was sub- 

 sequently treated 

 with iodine for the 

 starch reaction. 

 The area which 

 had been shaded 

 remains colorless/ 

 showing that 

 starch cannot be 

 formed without 

 the direct action 

 of sunlight, after 

 Noll. 



FIG. 18. The root of the 

 field bean (Vicia Faba) 

 thickly beset with bacteria 

 tubercles, after Noll. 



