134 



BOTANY 



to use free nitrogen of the air (ynth the exception of the nitrogen-fixing bac- 

 teria). See page 94. 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 get their food in different ways, they make it into living sub- 

 stance in exactly the same manner. 



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

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



leaves make three fourths of 

 an ounce for each square yard 

 of surface. A corn plant sends 

 10 to 15 grams of reserve ma- 

 terial 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. 



Evaporation of Excess Water. 

 — In the manufacture of starch 

 and proteid an enormous 

 amount of water is taken up 

 by the roots and passed to the 

 leaves to supply the needed 

 amount of mineral matter. 

 The excess of water, which often amounts in a single day to more 

 than the entire weight of the plant, is evaporated (passed off as 

 vapor) through the stomata. That water is passed through the 

 blade of the leaf in the form of moisture is shown by the follow- 

 ing experiment : — 



Experiment to show transpiration. Notice 

 that roots covered with root hairs have 

 grown out of the main stem of the plant In 

 response to the moist condition existing 

 outside of the riibber-covered flower-pot 

 and within the bell jar. 



