202 



EXPERIMENTS WITH PLANTS 



efficiency. In order to do its work of starch-making, 

 the chlorophyll must absorb rapidly large quantities of 

 carbon dioxide, as well as large amounts of energy. 

 The union of carbon dioxide and water under the 

 influence of the absorbed energy (sunlight) produces 

 grape-sugar, which is stored up in the form of starch, 

 or else diffuses out into the cells and thence to the 

 veins. The transfer to the veins is greatly assisted by 

 the funnel-shaped collecting cells (col.) and the con- 

 veying cells (conv. Figs. 113 and 114) . 



If we examine (with the high power of the micro- 

 scope) a section of a leaf which has been removed 



from the plant toward the close 

 of the day, we find the chloro- 

 phyll granules full of small 

 white glistening bodies which 

 turn dark when we place the 

 section in iodine solution (Fig. 

 116) . These are the small grains 

 of starch, which have been 

 formed by the union of carbon 

 dioxide and water under the in- 

 fluence of sunlight. During the 

 night they are again changed to 

 sugar, which travels along the 

 veins down into the stem and root. This movement 

 of sugar takes place during the day also, but the 

 sugar is then manufactured faster than it can be 



116. A single cell of a leaf with 

 chlorophyll grains (chl.gr) .con- 

 taining starch-grains (st. gr.) 



