THE CELL. 165 



colouring matter are embedded. The colouring matter 

 itself is chlorophyll, and may be dissolved out of the 

 granules, leaving the latter as ordinary protoplasm. 

 Almost without exception chlorophyll requires the action 

 ^ of sunlight for its production, and the chlorophyll dis- 

 appears from green parts when sunlight is withdrawn, as 

 is well seen in the process of bleaching celery. In many 

 of our brightly coloured foliage-plants the chlorophyll is 

 concealed from view by other colouring matters. In 

 flowers various colours are found in the protoplasm, but 

 these, unlike chlorophyll, are produced in darkness as 

 well as in sunlight. 



275. Chlorophyll is of the utmost importance to the 

 plant, seeing that only in the cells which contain it, and 

 in the presence of sunlight, can the materials which the 

 plant imbibes from the soil and the air be assimilated, 

 that is, converted into matter which the plant can use for 

 the purposes of growth. 



276. Now consider Fig. 214. Here are exhibited cell- 

 contents of an entirely different aspect. The rounded 

 bodies here visible are starch-granules, as may be easily 

 demonstrated by adding a drop of iodine solution to the 

 Potato section under the microscope, a characteristic blue 

 colour being at once produced. Such granules, differing 

 somewhat in shape in different cases, abound in the cells 

 of tubers and in grains of all sorts, where they have been 

 stored up for use during the process of germination. 

 They are originally formed during sunlight in the chloro- 

 phyll granules of the green parts. When the light is 

 withdrawn, as at night, they are dissolved and carried in 

 solution to other parts to promote growth or to be 

 stored up. 



