208 Education through Nature 



to unite with parts of water and carbon dioxide taken 

 in with the air and form proteids and starch. 



The starch is formed in little granules within the 

 chlorophyl bodies during the day. At night . it is 

 changed into sugar, which, being soluble in the sap 

 (Experiment I), is taken up by it. 



The sap of the leaf, having thus become more satu- 

 rated than in other parts of the plant, diffusion begins, 

 as in Experiment III, the sugar spreading out and 

 passing downwards into the stem and roots, where it 

 either serves as food for the growing plant, or else is 

 stored there as reserve food after again having been 

 converted back into starch. 



Growth. By the action of sunlight on the chlorophyl 

 the plant is able to make its own food from dissolved 

 salts, water, and air, and, by a process peculiar to all 

 living things, called assimilation, is able to convert the 

 food into its own substance. The result of this com- 

 plex process is growth. 



The bean plant increases in size by the roots pene- 

 trating deeper and deeper into the soil, and by the stem 

 lengthening out and carrying the leaves with it. It is 

 not definitely known why the stem grows upwards 

 while the roots grow downwards. It has been thought 

 that gravity, the force which causes an apple to fall 

 to the ground, may have something to do with it. 

 That this direction of growth of stem and root can be 

 reversed is shown by Experiment XIV. The up- 

 ward growth of the stem enables the plant to spread 

 its leaves out and thus expose them to more air and 

 sunshine. It is a clear case of fitness of things, evi- 

 dent adaptation to essential conditions, giving the 

 appearance of intelligent purpose or design. 



As the season advances it grows less rapidly, till it 

 ultimately stops growing altogether; but not before 

 developing new seeds containing little embryos, the 

 beginning of a new generation. 



