LEAVES AND THEIR WORK 



125 



potash). Proteids are probably not made directly into proto- 

 plasm in the leaf, but are stored by the cells of the plant and used 

 when needed, either to form new cells in growth or to repair waste. 

 While plants and animals obtain their food in different waj^s, 

 they probably make it into living substance (assimilate it) in 

 exactly the same manner. 



Foods serve exactly the same purposes in plants and in animals ; 

 they either build living matter or they are burned (oxidized) to 

 furnish energy (work power). If you doubt that a plant exerts 

 energy, note how the roots of a tree bore their way through the hard- 

 est soil, and how stems or roots of trees often split open the hardest 

 rocks, as illustrated on the opposite page. 



Rapidity of Starch- Making. Leaves which have been in dark- 

 ness soon show starch to be present when exposed to light. Squash 

 leaves make three fourths of an ounce for each square yard of sur- 

 face. A corn plant sends 10 to 15 

 grams of reserve material into the 

 ears in a single day. The formation 

 of fruit, and especially the growth of 

 the grain fields, show the economic 

 importance of this fact. Not only do 

 plants make their own food and store 

 it away, but they make food for 

 animals as well. And the food is 

 stored in such a stable form that it 

 may be sent to all parts of the world 

 in the form of grain or other fruits. 

 Animals, herbivorous and flesh- 

 eating, man himself, all are depend- 

 ent upon the starch-making processes 

 of the green plant for the ultimate 

 source of their food. 



Oxygen given off by Green Plants. 

 It is possible to prove that oxygen is 

 given off by green plants in sunlight. 

 The common green frog scum seen in 



, . ., . f , 111 Experiment to show that oxygen 



shallow ponds is often so full of bubbles is given off by grecn plantg in 

 that it is buoyed up by this means at the sunlight, o, oxygen. 



