22 



PLANT-LIFE 



are contained in carbon dioxide, which reaches the 

 chloroplasts from the atmosphere. But whence the 

 hydrogen ? This is undoubtedly derived from water in 

 the cell, for water is composed of hydrogen and oxygen 

 (H 2 0). So in water and carbon dioxide, the chloro- 

 plasts have the elements they require for starch manu- 



FIG. 8. CELLS FROM LEAF OF AMERICAN WATER- WEED (ELODEA). 

 HIGHLY MAGNIFIED. 



a, 6, c, d, e, Nuclei of cells; /, strand of protoplasm which crosses cell-cavity; 

 g, h, i, chloroplasts, some of which are dividing. 



facture. But they need something in addition to the 

 elements before they can achieve their alchemy, and that 

 something is energy: how do they get it? Well, we 

 know that carbon assimilation and starch formation are 

 dependent upon sunlight, and are sure that the chloro- 

 plasts get their energy from the sunlight. The fact is, 

 these tiny protoplasmic bodies somehow use the pig- 



