12 



THE PHENOMENA OF LIFE 



mass containing the nucleus and occupying the cell cavity. The inter- 

 stices are filled with fluid. In young vegetable cells such a distinction does 

 not exist; a finely granular protoplasm occupies the whole cell cavity, figure 

 12, A. As regards the respective functions of animal and vegetable cells, 

 one of the most important differences consists in the power which vegetable 

 cells possess of being able to build up new complicated nitrogenous and 

 non-nitrogenous bodies out of very simple chemical substances obtained 

 from the air and from the soil. They obtain from the air oxygen, carbon 

 dioxide, and water, as well as traces of ammonia gas; and from the soil they 

 obtain water, ammonium salts, nitrates, sulphates, and phosphates in com- 

 bination with such bases as potassium, calcium, magnesium, sodium, iron, 

 and others. The majority of plants are able to work up these elementary 

 compounds into other and more complicated bodies. This they are able 



FIG. 12. A. Young Vegetable Cells, Showing Cell Cavity Entirely Filled with Gran- 

 ular Protoplasm Enclosing a Large Oval Nucleus, with one or more Nucleoli. B. Older 

 cells from same plant, showing distinct cellulose wall and vacuolation of protoplasm. 



to do in consequence of their containing a certain coloring matter called 

 chlorophyll, the presence of which is the cause of the green hue of plants. 

 In all plants which contain chlorophyll two processes are constantly going 

 on when they are exposed to light: one, which is called true respiration and 

 is a process common to animal and vegetable cells alike, consists in the 

 taking of the oxygen from the atmosphere and the giving out of carbon 

 dioxide; the other, which is peculiar apparently to bodies containing chloro- 

 phyll, consists in the taking in of carbon dioxide and the giving out of oxygen. 

 It seems that the chlorophyll is capable of decomposing the carbon dioxide 

 gas and of fixing the carbon in the structures in the form of new compounds, 

 one of the most rapidly formed of which is starch. 



Vegetable protoplasm by the aid of its chlorophyll is able to build up a 

 large number of bodies besides starch, the most interesting and important 

 being protein or albumin. It appears to be a fact that the power which 

 bodies possess of being able to synthesize is to a large extent dependent 

 upon the chlorophyll they contain. Thus the power is present to a marked 

 extent only in the plants in which chlorophyll is found, and is absent in 



