Plants and Their Food 



have sunlight before they can make their food materials 

 out of the simple substances named. 



Ha. Food Materials Used by Green Plants. Use a jar filled with 

 clear spring water, as mentioned in 9a, but add nothing to the jar 

 but a small bit of some common pond scum, secured from the streams 

 or watering troughs. Place the jar in a well-lighted window, prefer- 

 ably a north window. Take care that the water does not get too 

 warm by staying too long in very bright light. Observe from day 

 to day to see if the alga mass is growing larger. It will grow much 

 slower than the yeast plants. The jar may be kept for weeks by 

 adding water from time to time, to make up the loss by evaporation. 

 If the alga grows, we must conclude that it gets all the food it used 

 from the well-water and air, because nothing else was added. The 

 water contains salts dissolved from the soil, and carbonic acid gas 

 dissolved from the air. 



12. Green Plants, like the pond scums, herbs, trees, 

 etc., that are able to make their food materials out of 

 simple substances, are called "independent," or "self- 

 feeding plants." Plants like the yeast, which must have 

 their food substances pre- 

 pared for them, are called 



"dependent plants." 



13. Cellular Structure of 

 Plants. The yeast and algse 

 are examples of very simple 

 plants. The higher plants 

 which we know as trees, 

 herbs and weeds, are very 

 large, but, if examined with 

 a strong microscope, we find 

 that their bodies are made 

 up of thousands, even mil- 

 lions, of tiny cells, much like 

 the cells of the algee and 



Fig. 5. Growth of individual ceils. A, 



celUwalL n ' nucleus " v ' 



